Maybe it's semantics, but I see "complain" to be different than "disagree". To that end there is a difference between having the "right" to complain vs. being "justified" in complaining.
So sure, you have a "right" to complain whether you bought it or not; but you're not really justified in that action unless you put money down for it.
But you can disagree with the product either way.
I havent' bought an EA game that uses Origin because I disagree with the service, restrictions, and how some vocal (complaining) players have lost access to their catalog. I fear any company having that power; that as I purchase more games I have more to lose if I speak up against something I find to be an injustice (such as DRM).
If enough sales are made, a publisher is initially not interested in the voice of those who did not purchase the game until the long tail starts and new market segments have to be tapped. As of today, EA is focusing only on those who purchased the game, because they actually fronted money to play. From everything I've seen, they've been doing an excellent job to, as quickly as possible, fix a really crappy situation; namely failure by their own success.
Now if the game was never initially purchased by the target market, and the reason gamers gave on surveys was "DRM", the studio would remove it, or at the very least scale back on how pervasive it acts. The fact is: the wide majority of gamers hate DRM, talk a good talk about how it's evil, but still shell out money because, as sconeu writers in a thread below, their mentality when told they should just abstain from purchasing it is, "'But then I can't play my shiny!!!!'"
So to the OP, no; we don't need a "Gamer Bill of Rights" because we have one right now: it's our wallet. Only purchase games that you believe in. If the DRM, ethics behind a company, or anything else that has to do with a game/publisher/etc... is disagreeable with you, simply don't buy their product. That's what I do. I look forward to seeing what indie makes a SimCity-like game that compares on it's level of fun; that's where I'll be putting my money, but until then I'll wait and find other games to play.