One of the overlooked things about O lines, IMHO, is system continuity. It's not just talent, but how well and how long that unit has played together. Find some really great offenses, like the Rams Turf teams or the KC with Holmes teams or the Vikings with Moss and Carter teams, you'll find O lines that were playing together for a while and had time to jell as a unit over a period of years with core mainstays as big cogs.
I do think better line play is part of the reason why Law Firm and Woodhead are able to be such a good rushing attack for them.
When the Giants won the Superbowl, that was a line that had played and jelled together for a while.
It all starts in the trenches.
It is one of the struggles of the Free Agency era, that FA has sapped lines from building and staying strong together over a period of years. Joe Montana was great for many reasons, I think one is that he knew he'd have Jesse Sapolu, Steve Wallace, Harris Barton, Randy Cross and Guy McIntyre and like playing together for a long time. Aikman could rest easy knowing he had Stepnoski, Larry Allen, Nate Newton, Mark Tuinei and Erik Williams playing together for a long time.
Keeping the Patriots O line unit together, with their tenure together, is not altogether a negative thing, albeit it might mean they will get long in the tooth together en masse.