Huge numbers of those CD keys are the result of credit card theft/fraud. Whilst you can grab yourself a bargain, the developer ends up paying. It is encouraged to use piracy over shadey resellers, even by some developers.

as much as i'd love to stick it to EA i would hate to enable a thief so i looked at this and the site claims the codes are basically greymarket re-distribution. i'm not sure i believe this but i also don't see how they are in business without the tacit consent of Microsoft, Sony and a half dozen others that could crush their ass.

It's also hard to see how there could be a mass scale of game code theft. Unlike credit cards there aren't millions of databases holding your details.