I think copy protections, if anything, endorse piracy, so a game must be of surpassing excellence to be purchased in its legal form.
My line of logic is - "If a game is good, the pirated copy is better only when copy protection is present, because in that case you don't get update compatibility and any key-dependent multiplayer, just for a lower price."
In my eyes, GTA 4, a game of undoubtedly surpassing excellence, is a prime candidate (rather, decided candidate) for pirating the moment it gets released, strictly because the game is good, it's out there and I can't play it on my PC, and that pisses me off. Supreme Commander, another game of surpassing excellence (at that point anyway) was much more useful when purchased, because the copy protection was removed straight away, leaving only the key for multiplayer access (that I didn't even need). For bad or even mediocre games, only the lack of copy protection can be an incentive to purchase them, because there's no point in buying what you don't like that also tries to force some rules on you.
I guess this logic is why I have so little purchased games, although there's also my dislike of russian localized versions to factor in. All in all, I probably have as little as 10-12 non-pirated games out of like 200 that I have stacked on the shelf.