I may have mis-spoke. I didn't mean reduce the number of powers just to have fewer; I meant that many of the powers would have to be removed or simplified in order to make the game work.
Ah, okay, I see what you mean. I'm not sure how much you know of WoW, so I'll just expand a little bit.
Types of things that wouldn't work in real time (wihout major revision beyond recognition):
1) Opportunity Attacks
WoW has some powers that are based on other things, in sort of a reactive manner. It wouldn't work for movement, but... well, I doubt anyone would care really?
2) Interrupts (unless they involve no choice to their effects)
Spell interupts are in WoW, there's other various reprisal attacks also.
3) Any "slide" effect (push and pull would still work)
4) Any "shift" effect
Sure, as written they wouldn't work, but again... this stuff is just 4e, so I'm not sure how many people would care that it was gone. I'm sure they could work a "slide" mechanic into real time, though.
5) Most of the Warlord's powers (esp. ones that involve granting attacks to allies)
Yeah, gone most likely. I'm sure a lot of this stuff would have some method of working it in, though fans of the material might not appreciate it.
Depends on the action of course. There would be no rounds, just cooldowns. Casting time/ interuption in WoW is drawn out sometimes, but compared to the D&D "round" being a longer amount of time, it's not that different really.
A 2 seconds casting time can seem like forever.
These are the things that occurred to me as fast as I could type them. I'm sure that a moment's reflection would result in many additions to the list.
The problem would be that fan's would nitpick about every little thing that they change for the format, really. If they replicate every class and race except Warlord, someone out there would say they messed it up and it's not D&D.
I do think they could get it closer to 4e than you would at first consider, but some concessions are required in any format.