My 2 cents:
Fast, large sweeping camera movements generate framerate hitches and are much more common with a mouse. These hitches are what distract you. That's not to say you can't tell and feel the difference between 30, 60, 120, even 2000 FPS, but a capped framerate is always better than a fluctuating one.
I first played through Crysis at 1920x1080 on a single 9800GT, maxed minus AA at about 20 FPS throughout. It felt pretty bad at first, but fighting the urge to turn settings down, I carried on and by the fourth mission I was fine with it. Just got used to it, I guess.
Generally the console offerings are developed around a cap of either 30 or 60, and this cap will not be the average but the minimum FPS (during normal play), achieved by sacrificing visual clarity. Titles which frequently drop below their FPS target almost always receive universally negative criticism for it, and this effects review scores. The PC version doesn't "matter" as much, so long as a chunk of PC gamers at that moment in time have a system which can average 60.
Dark Souls PC does not feel sluggish at 30, because it was designed to run at 30. GTA4 PC is similar. That iteration of the engine was designed around the 360/PS3, with a target of 30. Capping the game to a consistent 30 on PC makes it so much smoother than having it sometimes run at 100 and then suddenly drop to 30 in heavy traffic.