I think the problem for Edelman is really about formation flexibility. His strength is the quick hits and running after the catch, much like Welker and Hernandez. With those two players taking those routes, there are fewer Edelman to take, expecially coming back from injury.
Also, there really aren't many formations where we actually use 4 real WRs so far this year. Even in the empty backfield shotgun snaps, we've been lining up with Hernandez and a running back as two of the five (and Moss, Welker, Tate as the other three). This gives Brady audible options, as he can completely change gears to a single back 1 TE set with that personnel if the read calls for it. In that way, Hernandez has a little more value than Edelman when everyone is healthy.
In Edelman's favor though, is that he is a potential backup at EVERY receiver position, save Moss. He could play outside for Tate, or inside for Welker or Hernandez's slot duties. He can even knock out a few plays out of the backfield. His flexibility and the natural attrition of a long season will get him snaps. Right now we just have better options, which is a good problem to have.
Finally, the Bam Childress comparison isn't really fair, since Edelman has already had some productive regular season games in his career.
