Take a look at the WRs the Patriots have drafted:
http://www.drafthistory.com/index.php/team-position/patriots
Even going further back than the BB era, you have to go a long way before you find a WR draftee who didn't make it in NE, but flourished elsewhere. Then, take a look at the "big name" guys who came and failed. Guys like Chad Johnson and Joey Galloway didn't go on to have success once they went back to other teams.
Belichick's WR group has largely* been filled by:
2002 draft year
2007 trade year
Not counting last year's rookies, that's basically what the Patriots have been using for WR. I find it tough to blame anyone but the personnel department for something like that.
*Troy Brown was a Holdover and Patten was signed the year prior to the Branch/Givens draft. The team got one year each out of Reche Caldwell and Brandon LLoyd, and Gaffney was an in season signing the year prior to the Welker/Moss trades.