Technically...it's not the store's fault. If EA tells them that they're giving away kittens with the Battlefield 3 pre-order, they're not gonna argue.
If anything, they should protest by going to EA HQ or whatever is the closest thing to that.
On the other hand, such is the point of pre-ordering the game: to get extra stuff that you normally wouldn't be able to get somewhere else. If you're a hardcore fan of the series and you're planning on getting the game as soon as it comes out, why not pre-order it and get something for it? If you don't want to pre-order it, then rise up to the challenge and kick butt with the conventional guns.
I don't see why people are so offended; 75% of the pre-orders give you something extra that you can't normally get anywhere else, such as the MK costumes. Sure, some give you an advantage over other players while others are just for fun. But this doesn't come as a surprise. I see this as EA's way of saying "Hey, we're giving away goodies for the game and you can get into that starting right now even though the game is schedules to come out next year. So come get some". :/