I'm a huge ID fan and this is not an attempt to justify piracy, BUT....
First off.. I just heard on NPR yesterday that Video game sales exceeded Box Office sales last year. If true, the game industry shouldn't expect a lot of sympathy from their customers.
2nd... Are you seriously implying that ID could go out of business due to piracy? I don't believe for one second that ID (specifically ID) hasn't sold enough games to (a) remain in business) or (b) for all the founders to retire in comfort.
How bad do you expect kids to feel about copying games made by a company who did so well that most of the employees ran out and bought Ferraris after their first big hit? (perhaps I exaggerate but you get the point...)
Third, It pains me to hear you quote a $3 Billion loss figure and then say that's an under-estimate. I remain skeptical of piracy economic loss figures for this reason: JUST BECAUSE I OBTAINED A FREE COPY OF A GAME IN NO WAY MEANS I WOULD HAVE PURCHASED IT. Similarly, just because some Chinese dude bought your game for $2.00 does not mean he would have payed 50.00.
I treat software piracy loss figures the same way I treat RIAA and MPAA figures.... I simply don't believe them.
I've purchased every ID Game except Q4 which I borrowed & never finished. (do plan to purchase Q4ET though) I would have purchased Q4 if multi-player had offered more than Q3. Don't get me wrong, Q4 is a decent game but I rarely finish single player FPS games, and I preferred COD/COD2 for multiplayer at the time.
So here's how I rationalize my behavior and I suspect many out here do the same:
I've pirated my share of games but generally purchase the ones I really like, and/or titles from developers I think will deliver. I don't feel particularly guilty about having a copy of a game that I don't like and didn't play, in my possession. Occasionally I've not paid for something that I really enjoyed and I DO feel a bit guilty about this. I try to make up for to by frequently supporting independent software development via paypal donations, often when I don't even plan to use the software but just think it's cool.
I've also purchased many, MANY games that I didn't like, didn't play for more than 30 minutes, and couldn't return. I think this evens the score a bit.
I would also like to say this: When the majority of games are persistent, pay-as-you go, MMO type affairs, I will retire from gaming. I shudder to think what the real world is going to be like when all its inhabitants are completely absorbed in their virtual lives.