To be sure, these things are being way oversimplified (especially the history) and somewhat overstated. However, think about the Assassin. In AD&D, this is a class available to players in the first PHB. In later editions, never so. I can't think of any other core starting PHBs (i.e, first PHBs for that edition) that contained a class that actually required you to play an evil alignment. By 3E, we didn't even want to use the word thief.. they had to call them "rogues." Eliminating the "real" demons and devils in later editions...Please tell me what's "fatalistic" about Paladins and lawful good alignments? What's "optimistic" about the utterly bizarre (to my mind) obsession by modern RPGs with post-apocalyptic settings and vampires?
With the greatest respect, I think you're all taking out of your rears.
There are a lot of subtle differences... even in the art.. betw. AD&D and later editions. If you can't feel them qualitatively, I'm not sure I can explain it very well. 40ish guys like me never seem to require the explanation, we all get how the game just felt different after 2nd and later editions came out.
Gamma World is of course an oldschool game of the mid to late 70s that had many editions over the years.
Vampire, et al... I will confess I never played it and never read a rulebook. My sense of it was that it was mostly inspired by Anne Rice, which I read a lot of in the 80s and early 90s. When I hear about people's Vampire games, they always sound like gothy superheroes and dark conspiracy games more than actual grim, fatalistic horror a la Lovecraft. At this point, I really am talking out of my rear, so those of you who know the White Wolf stuff better should chime in on the OP's point.