Nice theory, but it's pretty obviously flawed. First, there's no evidence to suggest that nostalgia is the reason for this trend. Each generation has its own sort of design/style imprint on Pokémon building (I don't mean anything cosmetically, by the way), which could explain a generational gap. Example: defensive shift in GSC, especially due to the introduction of the Steel type, and prominent bulky Pokémon like Suicune, Skarmory, and Celebi. DPPt Pokémon are mostly offensively-inclined; lots of powerhouses were brought in, and due to the physical/special split and tutors, a bunch of Pokémon got a hell of a lot better. I'm not here to argue whether DPPt Pokémon are offensively inclined in general, so if you really can't see why I'm arguing that then you should look at the dex.
This late into DPPt (on the cusp of the fifth generation, years later from DPPt's release), we're already familiar with most of the Pokémon, so these Pokémon being 'new' isn't even true. DPPt is played by many more newer players than it is veterans; since the advent of WiFi, the better promotion and reception of the fourth generation, and the games' individual releases, Pokémon has boomed, and a lot of veterans have left. The stats mostly cover the majority: players of varying relative newness. However, the Übers tier has many older Pokémon, most of them being pre-existing bans carried over from past gens. While DPPt is very, very different from, say, RSE, it's easy to see why we aren't uprooting older Pokémon: it's easy to argue that most of the broken ones were banned in previous generations as is.
My last point is that Latias itself is from the 3rd generation. At the time of its unbanning, less people thought it was über than they do now. How does nostalgia explain the shifts in votes on Latias? The voter base is similar each stage. By the way, if you know the people in the voter base, you'll know that most did not play ADV at all or very seriously. But personally I think your 'explanation' isn't really very plausible and really has nothing to do with reality. Just my $0.02. ^^;