It's been an interesting couple of days at GenCon!
On Thursday, I managed to speak to Ken St. Andre and ask him when they began to use saving rolls in T&T with other attributes than Luck. He says that the idea occurred to him between 2nd and 3rd editions, which would would place it in 1977; originally, 'saving rolls' had been based only on Luck, and had been used purely for avoiding danger. During that time, however, he realized that the mechanic could be applied to other attributes... and that in so doing, it could be used to resolve active actions as well as reactions.
(2nd and 3rd edition were 'missing links' for me - I have the 1st edition reprint and one of 4th edition, but haven't had access to either 2nd or 3rd.)
He also says that he didn't get the idea from any other game, and that he's rarely looked at other RPGs, except for Runequest, which he had to read completely through while working on Stormbringer.
Given the timing, and that the version of the rules in Monsters! Monsters! didn't have the concept, it looks like Steve Jackson and Ken St. Andre may both have invented the idea of attribute checks independently.
Ken also stated that he suggested the idea of using percentile dice for resolution to the creators of Runequest.
Also available at the con was Metamorphosis Alpha, the first science-fiction RPG. I've picked up the "Collector's Edition", which has the original 1976 rules, errata for them, a collection of articles about MA (including a review from The Space Gamer and several supplementary bits that were published in The Dragon, The Dungeoneer, and The Space Gamer), and commentary by James Ward, Tim Kask, and Jon Petersen.
Since TSR took MA off the market after Gamma World was introduced (apparently feeling that two science-fiction RPGs involving mutated people, animals, and plants would be too many), all I've seen of it before this is the articles from The Dragon about it. I'm looking forward to digging into it!