I think it's whether he can maintain it over 82 games. After all, he hasn't been playing ~20min/game more than 42 games and had a serious injury that may or may not be a long term issue. Same questions for Emelin.
I guess it's interesting Bergevin is willing to still take that approach to re-sign despite what happened with Desharnais. Perhaps he's strong enough on his philosophy that one error won't rattle him.
Hopefully you have a link or something to back that claim up or else it looks like you made up stuff as proof to strengthen your argument especially considering Gorges was extended mid-season:
http://canadiens.nhl.com/club/news.htm?id=609302
He was playing 20-23 min/game, shutdown top pairing ES D minutes, top PK unit minutes on one of leagues best PKs, 'blocking machine' type name-reputation, etc for 4 straight seasons heading to UFA. I highly doubt this fellow would have approved much lower. Diaz is rumoured to get something close and he hasn't shown to be close to effective as Gorges at his best with a fraction of the experience.
If you want to speculate that perhaps the Habs offered him unreasonable term (especially considering shelf life of his player type) for a lower cap hit, then I can see the logic. Your claim that he'd have taken ~.5M discount had the Habs attempted to sign him earlier on the other hand, not sure it holds any basis.