My main thought is what's so devastating about a farmer making a critical hit with a rake? He's going to do what, 5 or 6 damage? That might mortally wound a goblin minion, but is going to do jack to anything the hero would fight. Depending on how much damage weapons, feats and techniques do at the epic level, which we don't know that much about, I would guess that the fighter's attack is going to be much more devastating.
It's true that if a critical hit represents a "perfect strike" that both characters have equal chances. I think that's fine. It just shows that there are things beyond the control of character skill.