It's not. It's private property, so the store would have to ask you to move, and they're not going to do that to a customer...I would hope.
Excellent... so park a big gas guzzler with anti-Obama stickers in one of those spots next time, lol!
I'll check out my local Whole Foods stores... I think they may have "Hybrid only" parking spaces as well. My car isn't a hybrid, but isn't a gas guzzler either (it's an old Toyota Camry wagon). I have plenty of anti-Obama stickers, though. ;-)