Not about games, but same thing applies:
http://imgs.xkcd.com/comics/steal_this_comic.png
Of course there is also another point to consider:
Would those who play pirated versions, actually buy the game if they couldn't get their hands on a pirated one?
All those game devs say that those people would buy their games, that's a doubtful claim.
Extremely doubtful even.
Great chances gaming has become so popular
because many could learn what gaming is about and can be fun via cheap pirated games.
[Edit]
Remember the times where every game had its shareware version?
One where you could play approx 1/3 of the game?
Now all we can get are some lousy bugged demos.
If you really wanna try a game out you must hunt for the pirated version, the 'official' demos are complete shit.
Worthless.