There are other things that I want to throw into the discussion. As pointed out many times before in other threads, thieves don't have the best attack bonus there are. So having that in mind:
A thief gets a better chance of bypassing armour if he is attacking a character that can not defend, because the DV he has to beat is 10+DR. This will be only if he gets someone flat footed, thus in a surprise round or the begining of combat, which is reduced to those particular two rounds, or when he manages to pull a succesful feint, which isn't that easy against more important NPCs, and he will only be able to attempt one feint per combat (Improved feint) or one feint per combat per opponent (Greater feint). So those are the chances for a thief, to deliver a moderately easy sneak attack that succesfully finesses. And it is usually one sneak attack per round, with the exeption of those precious moments at the begining of combat.
When a thief flanks, he can attempt to sneak attack with all his iterative attacks, but he has to beat the opponents full DV+DR. Given their not so good attack bonuses, he will have a harder time finessing through armour, and I could say he won't make it most of the time against the better armoured opponents, even with the +2 they get when flanking.
Thieves will often be lightly armoured, or wear no armour at all, they have fewer hit points and a bad fort save, so if you can't or prefer not to wear protection, it makes good sense to have Combat expertise to at least become harder to hit, lowering your own attack bonus in the process, so finessing again will be harder since you have to beat the higher DV+DR of your opponent.
So, with all the dificulty to find the ocasion to attempt a sneak attack, and to deliver it undiminished with a succesful finesse attack, why restrict it more? I don't think thieves as dangerous as they can be in Conan, challenge the place of soldiers or barbarians as the more menacing or skilled killers of Hyboria. They get their moments, but that's it, while the more martial classes are often unstopable killing machines.
Now, about sneak attacks forcing fort saves most of the time, soldiers have the b est fort saves in the game. In my experience, many of them have often made their fort saves against my sneak attacks, so that's another point that makes the soldier a tougher fighter, he has the stamina to endure even nasty wounds.