Don't they do that to encourage re-play? Everyone's like "OMG my game is only 80 hours long what a ripoff" otherwise. I don't play this kind of game anymore. No time, no time.
I didn't mean locked rooms or areas you can't access without lock picking skills or the like, I meant entire features of the game.
However, I've since found out that the reason I can't do what I want to do is down to a glitch rather than my perks. :-/