Yeah, it's amazing just how much your few moments of attention are worth to advertisers.
BF1942 is probably at the stage now where any existing copies will have to be destroyed, costing the publishers money, actually costing them more money to destroy them than the disks are worth. So it's better to pass them onto companies that can cheaply distribute them by other means. Adverts pay the website operators, who in turn pay for old games to give away to people visiting the site. Win win situation as long as the adverts don't annoy you.
Personally I think that a major problem is that people just don't trust these sorts of websites, with good reason. If I had a website like that, I'd get so simple flash games and offer things like BF1942 as prizes for doing well. That way people spend longer on the site, they trust it more because they feel the prizes are a reward more than a lure, and because of that people would return, if just to see what other games can be won.
Put this way, which would you be more likely to click on?
* A link promising a free copy of BF1942.
or...
* A link to a version of duck hunt but with nazi's instead of ducks, offering BF1942 as a prize for completing it.
I actually wish M$ would introduce some free offers - like a few gamer points for watching a promo or completing a game demo. This would be paid for by the game publishers - I'd bet an advert promising free gamer points on XBL for playing a demo would have more impact than a TV add. We pay at least £40 a pop for new 360 games, it's about time we got something for free from these gits.