Very funny. I guess if you wanted to find out what gamers were interested in the last place you would go to find out is locations where gamers hang out.
What makes a "poll" valid is the number of people you question.
Yes, but when you talk about going to a convention, you're already limiting your potential pool of interviewees from "gamers" down to "gamers who go to conventions".
"Gamers who go to conventions" are not the majority of "gamers".
Likewise, "gamers who post on EN World" are not the majority of "gamers".
Hell, these days, "gamers who visit gaming stores" may not be the majority of "gamers".
If you want to find out what "gamers who go to conventions" are playing, you go to a convention and ask the gamers there. Thinking that will be at all representative of what "gamers" in general are playing is foolishness. If nothing else, the original premise was "what games are being run at conventions", which is a distinct category from "what games do convention-goers play in general".
There are too many obfuscating factors. Some gamers go to conventions precisely because they get a chance while there to play different games, which they can't convince their home group to try. Any kind of organised play like the RPGA confuses the issue further, because the whole point of organised play is to get games happening when otherwise they might not be run. Some gamers play at conventions because they don't get a chance to play at all back home in Nowhere, Arkansas.
Broaden it beyond "games run at conventions" and you're still no better off. Gamers who attend conventions are, first and foremost, gamers
who can afford to attend conventions, especially once you get beyond local attendees and into out-of-towners who have to pay for hotel rooms. That's a separating factor from "gamers" as a general class. Gamers who attend conventions are also gamers who
want to attend conventions. They're a subset of "gamers" which excludes gamers who want to go but can't, or who can afford to go but don't want to.
Drawing any conclusions from even a properly-conducted survey at every convention in the world would be a) hard and b) misleading enough, much less the sort of screwloose "analysis" that involves looking at what games are officially run at conventions like GenCon.
It's just like sales data - people are arguing in this very thread that White Wolf games have a higher proportion of "readers" than "players" compared to other games. Whether or not that's true, the fact that there
are "readers" who aren't "players", and the fact that we don't have any reliable data on the proportions for any one game much less all of them, means that sales data is useless as well except as the very broadest indicator.
The same thing goes for anecdotal evidence like the number of books for each game you might see on your gaming store's shelf, or the number of books your gaming store's owner says he sells from each game.
If you want a proper analysis of what's being played, you would need to commission a proper poll, which would necessarily involve calling up a randomly-selected proportion of the population and asking them if they play roleplaying games, and if so which ones.
(Even then, you'd have to be aware of factors like gamer kids without their own phone lines and parents who don't know enough to identify the games they play, the extent to which randomly-selected people would be interested in participating in a phone poll,
et cetera.)