Dlichen, you are wrong on your critical damage reading. Under your reading you would not add feat, enhancement, or other damage bonuses to hit on a critical either since you are only allowed to add those bonuses to damage rolls (PHB 276). With a critical hit the maximized result becomes a proxy roll. With a vorpal weapon that means you get one "free" max roll and then get to roll the dice to see if you can continue the damage.
For plain game terms, under your ruling a Dwarven Fighter with an 18 Str, Wielding two hand axes +2 with TWF, and the Dwarf Weapon Training Feat would only do 10 points of damage (6 from hand axe + 4 for strength mod) versus the 15 points that the book states you would get (6 from axe, +4 str, +1 TWF, +2 DWT, +2 enhancement) on a critical hit.
Since the example on a critical hit (PHB 276) clearly supports the former, critical hits are a proxied damage roll.