And yet somehow, just about everyone counts Slater as a WR, so I'm not sure why we'd stop now? :
2013 opening day roster
Wide receivers (6) – Danny Amendola, Josh Boyce, Aaron Dobson, Julian Edelman, Matthew Slater, Kenbrell Thompkins
http://www.patriots.com/team/roster/Matthew-Slater/c78a0338-8e72-4dd1-b220-ef67bf22fb8a
All of the media counts him as a WR, the patriots.com official homepage counts him as a WR, and most of us will continue doing so for the exercise of trying to determine the 53 man roster.
If you are one of the minority that chooses not to count him as a WR for this exercise, then you could simply take one of the WR positions away, thus making the normal average 5 instead. The same principle is applied with Dobson, Edelman, Amendola, LaFell taking up all but one of the spots.
Of course some assume that we'll be keeping an extra man at the position this year, so that will be something to keep an eye on, and something that would obviously help anyone on the bubble such as Thompkins/Boyce/Gallon.