The last 20 years? Not much has changed at all really. Salomon and Look (race) are still using exactly the same designs with only cosmetic changes. I read a Salomon tech manual from the pre-spheric days, and they had that feature, they just didn't call it spheric. It seems their marketing department turned an existing design feature into a 'new innovation' by changing the colour of the AFD.
I think the reason behind the lack of innovation in bindings is that the DIN standards which govern the 'safety' of bindings only test very simple release modes to provide a pass/fail verdict, rather than looking at multiple complex realistic loads and providing a safety rating like we have with cars. The other reason for the lack of innovation is the perception among average users that all bindings are the same. As much as each manufacturer tries to say their bindings are better, there is some unwritten law that says they cannot provide PROOF that their bindings are better. And there are no independant organisations comparing binding designs so the only information that most people get comes from the manufacturers themselves.