That's right. Remove it. It's illogical, and causes more grief to those who don't wear heavy fort then it helps overall. It also causes unbalance in the game, because your expected to have it no matter what in the higher levels. Lower levels are more fun because of unexpected critical hits, causing those "Oh sh##!" moments. Instead of limiting the amount of crits, increase them, and increase the ways to increase a chance for a critical hit, etc. For example, increase the chance to score a critical hit if your attack counts as a sneak attack.
Replace it with something that makes more sense. Do not ever grant 100% immunity from critical hits, and don't include sneak attacks with it, those are completely different.
Seem like a radical idea? Because, it is. But it's for the better, I swear.
** However, I suppose that's a bit too radical for a game that is trying to stick to an already made set of rules. Even if I think those rules are...obsolete. I suppose it's better for this game, with it's unique standing, that fortification stays in. It's still needs to be tweaked tho, to allow for more versatility, and fun.**