Well, the extra hp go some way to help make sure that all those 'take it in the face' abilities won't actually kill the guy.. I think this is the scenario people are imagining for "it's broken":

Mithral Full Plate (it's medium) and a Heavy Shield. That's a base DR of 5/-; combine with the highest level Less Than a Flesh Wound and you have to be hit with 25 or more damage before any damage at all is suffered. Add +5 enhancements to both and you get DR 10/-, so the damage threshold is 30. You're also wearing +5 Full plate and carrying a +5 heavy shield, which means your base AC is 30 and is probably in the area of 43 (+5 Deflection, +5 Natural, +3 Dex). That's not usually too hard for higher level melee monsters to hit, but they have to worry about doing more than 30 damage per strike to do any damage at all, so they have to Power Attack. And if they Power Attack for enough to reliably do damage, chances are they no longer reliably hit.

Me, I don't think that's really broken. For the levels where it's actually achievable (with the class requirements as written, that's in *Epic* for the simplest entry and in the 15-20 range otherwise) melee characters need that kind of survivability if they're going to keep going head to head with monsters.