I think GNS theory (however flawed it may be), the 1999 WotC Market Research, or the material presented in Section 2 of Robin's Laws of Good Gamemastering all count as psychological models that didn't exist when Gygax created the game.
Oh, and hey, look here! Notable RPG game theories!
Certainly there have been mathematical insights that had not been applied to games by Gygax - each innovative dice mechanic counts, for example. As do discussions of "economies" or player and character resources.
And while it didn't provide any new mathematics to the academics, there was a time when nobody considered the tenets of mathematical game theory with respect to RPGs. Now, at least some do.
I view GNS as an attempt to articulate one version of a taxonomy that represents a single (then-advancing) style of play and distinguishing it from previous styles -- sort of like the "rules" around how post-modern art is distinguished from modern art or why Rembrandt was part of the Dutch Golden Age painting style versus Baroque.
Robin's Laws didn't talk about rule design so much as campaign/group dynamics from memory - it's been a very long time since I've pulled it out of storage so I may misremember.
While the poll may have certainly pointed out aspects of the game(s) investigated the then-current audience enjoyed/did not enjoy, it represents a cross-section of current attitudes from the audience -- in effect categorising their styles of play in ways that depended on the assumptions of the survey creators. In effect, it measured acknowledged participation through the lens of the author's style biases more than developing new objectively better criteria for game creation.
The variation of dice mechanics certainly counts as a stylistic change -- typically in an attempt to adjust what is emulated and how the emulation works is viewed by the players/characters, but they are not specific objective improvements in design. Rolling for powers in Villains&Vigilantes is different than buying them in CHAMPIONS, but neither is objectively better even though some players prefer one to the other. Spending dice from a pool feels different than making three checks at penalties, but one is not better than the other save in context of the preferences of the audience and if one option fits the style attempted by the creators better.
Player/character economies extend back the 2nd gen era (very early '80s) -- 007 James Bond, CHAMPIONS, et al. had player/character economies to one degree of another. Adding action points to a game doesn't objectively improve it so much as change the player experience. Some audiences appreciate the change; others are indifferent; still others dislike it.
Certainly more work has been done to articulate different styles. What we have today is certainly a richer stylistic environment -- it is much more likely a dedicated searcher will find a game that speaks to their preferred style than in late '70s, but the games produced this decade don't seem to be objectively better than those made thirty years ago. The assumptions have changed. There are different cultural stressors and inspiration sources today. Therefore game design has been altered to accommodate. But those stressors and inspiration sources will continue to evolve. Game design will as well so that new games continue to match current cultural attitudes.