To the original question, it is possible Rice has regressed due to his many leg injuries. It is also possible that before his season ending injury, he was still working his way back into form after his knee procedure during training camp.
What I do know with near certainty is that Rice has never been used by us/Wilson as he was with Favre in Minnesota. Favre was so confident of Rice's ability to make the catch, he often threw to Rice regardless of whether he was 'open', and more often than not, Rice came down with the ball. One only has to look at his targets to see that the same level of trust doesn't exist with Wilson. In case this point is argued, look at the number of times Wilson has thrown the ball to Tate in the past two years where Tate wasn't 'open' and needed to fight for the ball.
The one distinct time I remember Wilson throwing the ball up for Rice this year was in the Jags game. Wilson threw the ball into double coverage in the endzone, and Rice gracefully split the defenders and came down with it. I hoped we'd see more trust shown by Wilson where Rice is concerned, but for any number of reasons, it didn't materialize.
A receiver is only as 'dominant' as his QB allows him to be. How brutal have Fitzgerald's numbers been over the last few years? If Fitz had an Aaron Rodgers or Peyton Manning throwing to him over the past couple years, what do you think his numbers would have looked like?
On a related note: I'm grabbing Rice in my fantasy football dynasty leagues. I fully expect the Hawks to cut Rice at the end of the year. Assuming he can get healthy in the offseason, I also expect to see the NE Patriots sign the athletic, 6'4", (then) 28 year old in the offseason to a 3 or 4 year contract, and his numbers skyrocketing back to where they were under Favre (See Randy Moss).