I would like to have both available but I can see that the wheel would be much more beneficial for keeping the combat more active. If you think about it, it is difficult to keep using WASD at the same time you attempt to push on one of the F keys above or across the keyboard. If you set your items and spells properly with your mouse scroll wheel then it makes it so you can continue to move while switching instead of stopping dead in your tracks even for a millisecond to switch hotkeys. I would assume this would be more beneficial to PC users but if I remember correctly hotkeys were pretty annoying in oblivion for consoles. Didn't you have to hold something down first before selecting a hotkeyed spell or weapon? If so that is much more difficult than just pushing on the D pad.
I think on the 360 to assign something you had to press Y and the direction on the d-pad you wanted to bind to. To actually use the hotkey you just pressed the corresponding direction on the d-pad but the diagonal detection was abysmal.
Anyways, in Oblivion wasn't the scroll wheel one toggle for third person mode? With zoom adjusted by scrolling the wheel? How would you handle zoom if the scroll wheel is used up by hotkeys.
Besides one of their goals is making each of the combat styles more distinct, and making two handers unwieldy to use for all except pure warriors would serve that purpose excellently.