Yeah, I mean would Chuck Knoll have four Super Bowls without Greene, Lambert, Ham, Bradshaw, etc.? Would Jimmy Johnson have two Super Bowls without Aikman, Smith, Irvin, etc.? Even great coaches need players to win games.
The fact of the matter is that in 2007 the Pats any one of three plays away from going 19-0 without McGinest, Johnson, Branch, Law, etc. In two of the three Super Bowl wins, the Pats were one field goal kick away from turning a regulation win to sending the game into overtime where anything could happen (and if the Pats lost the coin flip against Carolina they probably would have lost since Harrison and Wilson was out and Ty Law claims the Pats would have also lost to the Rams in the same scenario because the defense was spent). So we really shouldn't say the reason the Pats haven't won a Super Bowl since 2004 is because the they let guys like McGinest, Law (who basically missed most of the 2004 run anyway), Branch, Johnson, etc. It is a little disingenuous.
Besides, you can't hold onto players forever. Teams who tried have crashed and burned pretty bad. Look at the Cowboys and 49ers of the late 90s. The Rams fell apart this decade too. The Raiders although never sealing the deal held onto that aged team for far, far too long and Davis has continued to screw it up because it fell apart so fast and he is desperate to totally rebuild every year (although the problems with that team run far, far deeper than not knowing when to start to replace parts).