Wrong, Rodgers has been "learning", preparing, sitting, the successor, whatever you want to call it, for only 3 years. 2 of those years the Packers were held hostage by Favre and his retire don't retire bull shit. How could they trade him? Who would have been their QB? Trading a guy you drafted with the singular purpose of succeeding Favre is retarded unless you (i) get someone young who you think is better; or (ii) find out he sucks.
Neither has happened, what would make you say he has "rotted" on any bench? The list of QBs that had high level success in their first three seasons out of college is far shorter than the list of those that didn't have success until after that third year. Many, many QBs "rotted" for a few years before starting and went on to have good success. To wit, and just off the top of my head:
Hasselbeck
Brunnell
Brad Johnson
Rich Gannon
Philip Rivers
Delhomme
Bulger
Warner
Garcia
Aaron Brooks
Derek Anderson
And whoever said Aaron Rodgers is "injury prone", he never missed a game in college and, albeit he is not playing, hasn't been injured since.