Huh? I don’t follow you here Mark, how does bundling two discs together defeat the purpose of getting the collection where putting both games onto one disc doesn’t?
As for why the seperate discs, certainly being able to loan one like you mentioned out is a good reason, but it also keeps each game’s package art seperate, it prevents uninformed idiots from claiming that Rockstar cut down the games to fit them onto one disc, it allowed Rockstar to add more textures, music, etc… to each game. That said, I can also think of good reasons for putting them on the same disc, production costs, save space, etc… but I don’t really see any reason to make a big deal out of it, and I certainly don’t see how it defeats the purpose of, well, anything. You can even throw away the cardboard sleeves that holds the two games together if you think it defeats the purpose of your Xbox game organization.