Well first off, I didn't take Mearls' article on the gnome to indicate that there's a mandate for a race if 10% say they want it. What he was getting at is that its not a simple as saying "Well if only 10% of people want something, then its not important as it won't affect very many people." He was merely pointing out that if 10% of players want gnomes, then on average, 50% of D&D groups will have somebody wanting to play a gnome. I don't think that there was ever a suggestion that they should ignore the other 90%, nor that they should ignore a race that say 75% of players love. Just that 10%, in the context of D&D, is actually much larger than it seems.
Anyway, back on topic, I think the problem with your take on the poll in this article is that you are assuming that not only is balance the very most important thing, but that everyone (or just about everyone) agrees with this principle. You then take the assumption that if the first choice is not a 98% selection that WotC will then absolutely throw balance out the window (which is certainly not confirmed by the article).
To me, fun is the most important factor. Balance affects fun, but it does not guarantee it. This is evident by the fact that I've really enjoyed every edition of D&D that I've played, which includes a little bit of first, a fair amount of 2nd, and a lot of both 3.x and 4ed. The degree of balance in these various editions has generally changed quite a bit, but I still have fun.
Personally, my view is that if either of the first two choices are the front runners (and particularly if they are the top two) then the message is sent that balance absolutely should be looked at and considered. If the third choice is the frontrunner, then balance should be considered, but its only one of many factors that need to be looked at (and those other factors definitely need to be addressed). If the last two choices become the front runners then yeah, I guess there's some merit to the idea that balance is not all that important in a PnP RPG. Of course, it still needs to be acknowledged (as it has been by Mearls) that these polls are far from scientific, so any surprising results (such as "Who cares about balance?") should definitely be looked at carefully before being used as guidance for the game.
For the record, I went with the third choice because while I whole heartedly believe that balance CAN make a game more fun, I don't believe that either a) it automatically makes a game for or that b) a lack of balance guarantees that the game will not be fun. Certainly, if you are going to create a game that does not enjoy balance between the classes, I think you have your work cut out for you in order to make it fun, but it can be done. Its easier to make the game balanced, but not mandatory.