8 according to Mike Reiss, all are starters:
QB - T. Brady
WR - W. Welker
TE - R. Gronkowski
LG - L. Mankins
RG - B. Waters
DE - A. Carter
DT/NT - V. Wilfork
ST - M. Slater
Hernandez was edged out by Gates, total snub IMO.
Gates - 59 catches for 672 yards (11.4 avg, long of 27) and 6 TDs
Hernandez - 72 catches for 772 yards (10.7 avg, long of 46) and 6 TDs
This is called getting in by reputation and/or being overshadowed by a beast named Rob Gronkowski.
Arrington was edged out by Bailey, Revis, and Joseph.
According to Reiss, Arrington has allowed the second lowest QB rating in the entire NFL when QB's threw at him (Revis was #1) and he is currently tied for 1st in interceptions.
Can't argue with 8 being valued as the best at their positions in the AFC, but I believe it should have been 10.
Edit: 8 on Roster, 7 are "starters" as STers aren't counted as starters.