The reason I see pirating existing is a lot of games just completely suck ass, and they cost $50+. Hell, look at Sins when it first released. It was $40, I got it release day at Gamestop and it was mostly a mess. It didnt have a campaign, the online was unstable, and the AI was crap. It was a fun game, I'll give it that, but for $40 I felt ripped off. Look at entrenchment... On release day (Original release, in November), the beta was a complete mess too. I'll give Ironclad or Stardock credit for owning up and delaying the release. Now, look at RA3 or CnC3. Both were shit, and both never got better. I bought RA3 for 35$ on sale, and regretted every dollar of it. Some games are great, but most are only ok, and for every good game there are 5 bad ones trying to steal your money. Since most games dont have demos, it can be hard to find a way through the marketting BS to get a good game. Pirating basically lets you try the game before you waste your money on it.
While I dont actively download games, I will try a pirated game at a LAN party or friends house. If the game is good enough for that, 99% of the time I'll be buying it soon.
If game companies really want to do away with pirating, they should make better demos, and give a return policy, or admit that some games arent that good, and charge less for them. I can definately think of a few games recently I've purchased at full price that are worth the cost, namely DOW2, Company of Heroes, Fallout 3 and Sins. Other then that, most have been dissapointments.
Almost any other product I can return for a refund (minus restock). Even movies I've been known to leave early and get a refund, or a free ticket. I dont see why games should be held to a different standard.