You'd have better luck going to the Apple store. Best Buy will take your iPad, compare it to one of the demo units or one of the mobile checkout iPads that the associates use, and say because the comparison units have the same thing, which they will, they won't be willing to take a chance on Apple not taking it back, thus they would have to eat the cost of the iPad. Apple is a little more lenient because they are the manufacturer, and can turn around, 'recondition' it, and sell as a refurb. So they are not as sensitive to a return, but you still have to dance with some of the Apple store geniuses if your claim is more nit picking than anything.
Unless it is absolutely horrible, you have to realize that LCD technology is not 'perfect' and that some bleed is going to be encountered. Its the same with $2K television LCD's, so why wouldn't it hold true for a small iPad? Samsung would tell you to jump in the lake if you continue to ask for a 55" LCD screen replacement after they replaced the first on good faith. Amazon will do the same.
I've seen 7 iPads, and they all had 'some' bleed. This is just the nature of the beast. Anyone who says their's is 'perfect', then they just aren't as sensitive to it as the next guy. Mine has a very tiny bit at the bottom of the screen when in portrait mode, but nothing to complain about. The screen looks fantastic.
However, this doesn't mean that if you legitimately have an overly excessive backlight issue, that you don't take it in and get a replacement. If you are nit picking, that is something entirely different. Only you can make that determination.