I think it is more about the convenience of having the display work through HDMI. On the 790 how does on screen work if your connections are through HDMI?
the biggest improvement with the 890 in this respect is that you get OVERLAY of the OSD/GUI. On the 790/1910 (and older models), what happens is the video blanks out to a black screen and then your TV has to re-sync to the OSD. depending on your TV you may get a delay of a few seconds (just like when switching between an HD and an SD channel on cable).
so you still get OSD over HDMI, it just doesn't smoothly OVERLAY on top of the video.
Specifically, I thought that the processor would perform judder reduction for 24fps that my plasma does not do...
judder reduction is difficult if your TV is stuck playing at 60Hz regardless of the input signal -- better video processing can help but the bottom line is there is no "smooth" way to squeeze 24 fps material into 60 frames for output.
have you taken a 1080p/24 input, and compared how it looks going straight to the TV vs being processed to 1080p/60 by the Denon AVR? specifically, with slow pans in a movie where "judder" can be pretty apparent?
I'm curious about this... but I think the bottom line is that the only TRUE solution for film "judder" is to get a display that can refresh at a multiple of 24fps.
the 890/2310 model (with ABT-2010) appears to be able to cross-convert 1080p/24 > 1080p/60, whereas the lesser ABT chip in the 1910/790 model looks to just pass it through untouched.