I've heard the same story about the current year's training camp being tougher than the previous one since the 2006 camp. That's what I base my "gettting tougher" statement on. This started in response to the 2005 season. It has nothing to do with 2001-2006.
You might find something about the conditioning drill in The Education of a Coach, or Patriot Reign, or The Blue Print. I'm pretty sure one of those books mentioned that after he took over from Pete Carroll, Belichick put the team through a conditioning drill which was considered pretty basic with Parcells's Giants, Pats, and Jets. Many of the players struggled with it.
Also, I don't know if they'll make it to the Super Bowl, but making it to the AFC Championship is quite an accomplishment for the Jets. See if you can find some stories about their training camp this year comparing it to camps under Mangini. I underestimated the Jets. Part of my disdain for the Jets was hearing about Ryan's much more laid back camp. Again, a team eases up and does better late in the season. (I mistakenly thought they were taking it too easy, I guess.)
Our team looked like it consistently wore down late in games all year. Plus, look how it finished. The Pats were 4-5 in their last 9 games after a 6-2 start.
Neither of us are at practices, so we're trying to figure out if they've been working harder or less hard based on limited information. My point is that IF they've been making things tougher since the end of the 2005 season, then maybe it's time to try something different.