Maybe. Having made so many wrong statements about this I don't want to stick my neck out again... but it seems now the most likely culprit is the way that recordings are created and stored. So, changing this would probably take a rewrite of the filesystem followed by a lengthy time after a download where the DVR was unavailable because it was moving files.
Well, if we are going to speculate I'll chime in with my own. I have years of experience reverse engineering the software on black boxes so have some related experience. I'd have to guess the designers chose to "discard" some of the incoming i-framesets rather than trying to control the output frames to the TV. This would make the output jerky no matter what you did. You could just discard more sets to move forward faster. The end result would be that all FF speeds would have the same level of jerkiness but move through the picture quicker - which is exactly how the D* software boxes behave. This contrasts with how Tivo boxes appear during FF at all speeds.
The only solution would be to rewrite the entire FF code around the output from the chips - likely not a trivial undertaking if you didn't start out that way.
In the end it doesn't matter why or what. What matters is how the FF works for your particular purpose. I like silky smooth FFx1 so prefer Tivo in that regard.
I suggest we stop speculating - it's not really helpful.