SilentMRG: These are the complete games. And there is no illegality in this, GTA and its expansions are no longer for sale and Rockstar Games no longer cares about the first two in the series. Maybe you don't know, but there was a time when the first two were free on Rockstar's own website, and they were removed and forgotten, as far as I know for no clear reason. Thank goodness there are fans to preserve the history of games. ;)
amok: The fact that Rockstar no longer sell the games, does not make it legal for you to pack them up and offer them. Rockstar still owns the rights to the games, no matter if they sell them or not. The same applies to the short time they gave them away for tree on their website. Since they own the rights, then it is also within their rights to do with them what they want, including giving them away (on their own website) for a short time. This does not mean you can do the same, the games did not become freeware.
The problem is that gOg is a buisness, and it is illegal to have links to illegal games on their website, they are trying to get partners to sell games here, so they need to be seen as above board.
There is an argument for game preservation in making sure that software is available and do not get lost, which is important, but gOg as a buisness cannot and should not have those links on their forum. There are other sites that do so, which does nont have that legal and corporate visibility / reputation
edit - Think of this. Last week, gOg gave away The Beast Inside here on their website. This does not mean that The Beast Inside is now freeware, and you can copy and distribute it to your hearts content. that would still be piracy.
I'm only going to tell you two things, because I'm tired of explaining what piracy, fair use, abandonware, among other things.
The following is:
1 - The guys who did this are not making a profit, they are not selling. It's just preservation and nothing more.
2 - The link is not direct, the link is to the GTA forum, a very well-known forum by the way. So there is nothing wrong with the link, if you think it is wrong for whatever reason, just don't click on it, or click and don't click on the link that leads to the package, simple as making pie.
Cheers! ;)