What I want to say is,I agree with the previous post on the point that this is a game and several things should be altered to make it fun,even if it's against physics of real world.It's also impossible to chain weapons swings with the speed we can in the game.Or use a dagger at 200 stabs per minute.
I've seen videos of people (like in real life, not for a movie) swinging swords around in staged fights (with real swords) faster than in Oblivion. Swords were actually very light. The Oblivion speed for this is not really over the top at all.
The boomerang thing is way out of the realm of possibility for having it return to you after a strike, and the attatching knives idea? Don't get me started. Todd said they wanted to avoid many of the more ridiculous things that Japanese RPGs tend towards.
EDIT: Though a non-returning, non randomly adorned boomerang could be quite an effective weapon in skilled hands.