It will not help tournaments, from your perspective.
It will help Nintendo make more money through promo lift and customer retention.
I'm trying to point out that, if someone were to do complex database analytics to determine how many tournament locations there should be and where they should be held, there will most likely need to be a financial incentive. Why would they spend money on analytics if there isn't money to be made?
Financial incentive is tied back to who buys the games, and how much money they spend on the brand in general. This could also be cards and other items like plush toys or whatever, but the games are some of the best-selling games on Nintendo systems. Seriously - would some of us even own a Nintendo system if it weren't for Pokemon? How many people who buy a console and own a Pokemon game (or two) also go on to buy other games? Are the people who buy (and register) Pokemon games more loyal than customers who don't (e.g., did they stick with Nintendo during the lean "Gamecube" years when the big N was in last place during the "console wars")? I would be willing to bet a not-insignificant amount of money that Nintendo is asking - and using data to answer - these questions. If Nintendo is indeed just handing off the tournaments to card-game people entirely (and I don't think they are, if they give out promo downloads like the Life Orb Milotic), then they are missing a marketing opportunity, and I don't think they're likely to do that.
The place where that is kept track of (systems and games) on a per-customer basis is the MyNintendo accounts. This can be linked back to demographics (rented from Dun & Bradstreet or some other data clearing house) - average household income, how many kids, how much discretionary income, home-ownership rates, level of education, and so forth.
This DOES work for Nintendo. It would not in any way, shape, or form be "outrageous" to place tournaments based on the number of registered games - companies exist to make money, not to do charity, and Nintendo more than most. Seriously, why do you think they started doing product registration in the first place? At this point, the tournaments are purposeful for the game makers and publishers largely insofar as it builds the brand and encourages future product loyalty and increased sales. There is no registration fee; the tournaments are not self-supporting. If they did institute a fee, this would change the entire equation - but right now, this means they need to make money elsewhere (i.e., on you buying more games). Your entry fee is, in effect, the game that you buy - buy the game and you, too, could become the next World Champion! The reason you even have Pokemon tournaments and not "Mega Man Battle Network" tournaments is because of the popularity (and sales) of Pokemon. It's entirely plausible that they have done something like see where the greatest concentration of people who own Diamond + Pearl + Platinum is located and thought to themselves: "let's keep these people involved with the brand, because this means they're likely to buy not just HeartGold but also SoulSilver."
Shelley Lazarus of Ogilvy & Mather said once at a DMA conference keynote speech: "If it doesn't produce measurable results, it didn't happen." Yes, some of those codes go into the trash, but guess what? The ones that don't belong to the customers that are most engaged with your brand. Those are the ones you care about because they most likely make you the most money - money that you can measure. Those are the people you want to please and encourage with special events - say, a tournament (or a giveaway like the JAA tour or Pokemon Rocks America). Why do you think they have these events a year or so after the games come out, and not immediately? It's probably because they want to keep people engaged with the Pokemon brand in the 2-3 year gap between releases. Platinum is most likely getting its promos right now because HeartGold and SoulSilver are right around the corner, and they want people hyped up for its release. Now that some promos are being given away by WiFi, there's a better-than-average chance that they're attempting to match up IP addresses with locations (a very imprecise business, but it's better than no data at all - and remember that you can link your DS' online identity to your MyNintendo account, which is much more precise) to see where those customers might be, too.
So don't sit there and puzzle over why King of Prussia got a tournament and NYC didn't (or, for that matter, why King of Prussia and not downtown Philly?). NYC gets engaged with the Pokemon brand by the Nintendo World Store, all day, every day. King of Prussia sits right near the wealthy "Main Line" area of Pennsylvania - where people have lots of money to spend on products. Not saying that this was absolutely and necessarily the reason, but it seems like a plausible one given the financial incentive.
It's not just the number of people they want (although I'm sure that's nice) - they want good customers, or people from demographics likely to be such. I'm not sure what the numbers are exactly, but if some marketing person, somewhere, in one of those companies isn't getting the data and figuring it out, they are lying down on the job. Pokemon Company, Nintendo, whoever - and you can bet they collaborate; it's not like they're in competition...Nintendo and Pokemon are in a symbiotic relationship, and the future success of both is intertwined with one another in many ways. Do you seriously think that if GameFreak said to Nintendo "we'd like to see something like X in your next hand-held console," Nintendo wouldn't sit up and pay attention? For instance: did any other game even use the IR port on the Game Boy Color besides Gold / Silver?
I am sure that, at the very least, they have a bunch of stats on all the events they've run in the last five years at the various locations: how many people came, how many promos they gave out, etc. One of the big reasons they may give out only one promo Pokemon per cartridge is the fact that they can then measure how many cartridges out there are still being used, and they have estimates on how many people who own one cartridge (and continue to use it, vs. people who sell it back to Gamestop like you indicated) are likely to go on and buy the next game in the series.
The Pokemon franchise, with its promo Pokemon and events and all that, is a database marketer's dream come true. Or did you think there was some other reason why the one-per-generation promo characters from gens 1 & 2 jumped to 2 for Gen 3 and what...three for Gen 4? How many copies of Pokemon Ranch do you think they sold just because you could get Mew? Or how about this one: why don't they let you download a Mew or Celebi for RBY/GSC now at the Nintendo World Store? I mean, it wouldn't hurt anybody, would it? But they've created a structure where you have to buy the games and keep up-to-date with the promos while the games are still near full-price, or you won't be able to complete your Pokedex. You can't buy a Pokemon game used at Gamestop five to ten years after release (when Nintendo doesn't see any of the money) and have access to the full range of fun.
Unless you use a GameShark, and if you do that, then guess what - you run the risk of being disqualified for the tournaments (or banned from the Global Trading System), don't you? Gotcha.
You need to start thinking like a business before you go around saying certain ideas are "outrageous."