I'm not sure that he so much tamed down, but I do think he acts a bit different. Like you said, we're never going to see Frank's Animal again, now it's Eric's Animal, and it's obvious that each performer has a different interpretation of each character.
I've noticed that The Swedish Chef has been tamed down. Remember when he'd chase chickens and turkeys around with meat cleavers? Now he hugs chickens. It's a good thing Gonzo doesn't seem to notice.
I'm glad he quit chasing stuff with cleavers...I had too many of my friends asking me who the guy who runs around chopping people's heads off is...(seriously...)