After reading some of the replies already, my anser has pretty much already been given, but since you asked for one, I do believe it is a good thing to have it capped at 50 to avoid over powering everything. If you could go beyond that, you would just have a character that was good at everything, and to me, there is not much fun in that, less the game can balance it properly to keep things challenging. At the end of the day though, we really wont know much till the game is released so we can see how the mechanics of it work.
You say this now, but are you sure you would feel the same way if you reach level 51?
From the interview with Todd, it seems very unlikely that most people would ever reach the mathematical level cap, so we are really talking about perhaps just a handful of perks, up to whatever level would be the natural stopping point for a character after you have played for 400 hours or so. (That might be level 60, or it might be level 40 or 50. No way to tell at this point.)