Well, you're wrong.
Not being snarky, I just did both extensively now and prepping for 4e is considerably faster faster, period. Fights themselves are somewhat faster. Not to as great an extent as the prepping, but still noticeable so (though you need to get used to it first).
I tried to read a 4E adventure, and *every* room took me something like an hour to "get" (i.e. how the monsters and traps et al. work "together" and how the encounter should be ran from a tactical POV). Maybe I'm just not tactically-inclined enough to run 4E?
Also, it's probably a lot faster if you just use existing monsters, traps and skill challenges. I think it'd feel quite intimidating if you try to create your own stuff for the first time. But, as SC noted above, once you "get" the system, you can use short-hand notes or run stuff "on the fly".
For the record, I'm considering about participating in a 4E campaign (despite what my friend said). The trouble is, I only know of one 4E campaign in the town I live in (and I know a lot of gamers here). So I'll probably have to join the same group eventually...