Is Wobbuffet allowed in Japan? Granted, this is PBR, where Ubers are not checked, but I saw one on a Japanese team. Is Wobbuffet frowned upon in the East like he is here?
No, it isn't. Wobbuffet isn't terribly useful in 3v3. It's also very unlikely they'd ban something that GameFreak themselves wouldn't.
EDIT: I checked the Friend Pass a few minutes ago, and he has OHKO moves on Walrein and Dugtrio (same guy that had Wobbuffet). Do the East Asians have an OHKO Clause?
I've seen quite a few OHKOs used on teams with properly EVed Pokemon, as well as Double Team. This was both on PBR random and NetBattle back in the day, vs. players with the JP tag in their name.
Contrary to popular belief, random battles do tell us quite a bit about their metagame, so long as you don't face a player that has, say, 6 Darkrai on their team. If you find someone that's using a Latios, properly EV trained, with five other strong Pokemon, and it isn't holding Soul Dew, you can assume that the player was probably building a 'standard' team and opted not to use the item simply because that would make their team 'Uber'.
China's a hell of a lot different though. Whereas Japan is very much about keeping the game as similar to its roots as possible, China is content with banning anything that sounds slightly overpowered, even on paper. (To be fair, I here their metagame is actually really fun to play.) I guess the Western metagame is the central point between the other two. When I say Western, I mean North America, parts of Europe, New Zeland, and Australia, in other words smogoners.
It's no surprise, really. Unless there was one dominant community that governs this game, I don't see how you'd expect each community's metagames to look exactly the same.
I can't pinpoint the exact origins of competitive Pokemon, but I'm pretty sure tournaments started in Japan sometime around the introduction of Pokemon Stadium. Rules like Species Clause, Freeze Clause, and the 3 Pokemon only rule were introduced in that game. In the standard cup, there was also a rule that restricted your levels between 50 and 55. In ADV it was just changed to 50. IIRC, they actually used things like level 52 Tyranitar in Japan back in the GSC days.
If Japan was exposed to the tournament scene that early, then it's likely that they'd want to base their "underground" metagame around the official ruleset. Though I've seen a few arbitrary rules like no Latias/Latios/Cresselia, and according to one of skarm's old threads, Heracross was banned in ADV and you could only have 1 Hidden Power user on your team. I'm not too sure if this was ever confirmed though. One thing I've noticed about Japanese casual play is that they tend to use a lot of gimmicks.
Over here, the 3 Pokemon rule and the level restrictions were completely ignored so we could develop our own rules. Preference seems to be heavily based on tradition. The tournaments that have occured had really obscure, abitrary rules anyways. There were no items in the 2005 Seattle tournament, for example. Casual play in North America is almost identical to our tournament style of playing. As a whole, I think we take the game a lot more seriously.