I see it the opposite way. When the coaches were pulling Ricky in the 2nd half of games that we already had well under control, it was to my recollection Travis Minor who was receiving the bulk of handoffs. When it came to changes of pace, however, the 3rd down back's role, it was Robert Edwards who got the ball.
A lot of people have trouble understanding trade value is not just based on the player its based on the situation. These are the same people who couldn't believe we were only getting a 7th for a perennial starter like Derrick Rodgers or that we had to pay a 4th for Jay Williams.
Its the situation, and as things currently stand not only is Robert Edwards being phased out of the 3rd down back role by Ricky's increased role and Charlie Rogers' work in the backfield, but now the coaches are starting to turn on to Leonard Henry a little more and really want to give him a good look and they drafted Travis Minor in the 3rd round anyway to be a good backup RB which he's shown he can be. Thats the situation. And the situation in Tampa is that even though they need a RB badly now, there's guys who are less of a question mark from an injury standpoint out there than Robert Edwards and the Bucs could easily just say "Ok, forget Edwards we'll just go with Bettis...or Dayne...or Jones."
We won't be missing Edwards nearly as much as you think and he wont be missing us all that much either because the guy wants a shot at a premier role on some team and this could be a great opportunity for him.