Interesting -- my experience, at least with mid- to high-level casters, is the very opposite. For 1e through 3e, a caster had this huge panoply of spells, and to understand any of them, you had to flip to the page in the PH that listed the spell. By contrast, in 4e, casters have a smaller list of spells with concise effects, each fully described on the power card/character sheet.
I never wanted to play a caster in previous versions of D&D because I didn't want to have to memorize the strengths and weaknesses of literally dozens of spells in order to be effective. By contrast, when playing a 4e character, I can quickly skim my short list of powers to know what might be a good idea at the time.
I played a 4e wizard for the first time over the weekend. I had basically no understanding of the 4e wizard powers beforehand, and I got by just fine.
I think a lot depends on the particular player and class though. I agree that 4ed wizards are generally much less complex than prior editions, but at the same time, the non-essentials martial classes are far more complex with many more options available. All the added feats, abilities, powers, etc. make for a much more complex character -- particularly if you choose feats or powers that give conditional modifiers.
Now personally I feel that more options is gold. After all, the more options you have, the greater the ability to create a truly unique character. I don't want every fighter to look and play the same, I want to see somebody's personal spin on that class. However, if you are a Tactician type player, the extra options can actually be a hindrance as you agonize over every action (something I've seen more than a couple players do). When dealing with tacticians, its sometimes nice for them to have to say "I guess I'll try to bash his face in." as opposed to "Well, I could go here and use power X which might hit these 3 guys for small damage as well as knocking them prone if you want, or I could over to this square and use power Y and deal slightly more damage to these other 2 guys, but they won't get knocked prone . . . oh, but they will take a -2 to hit. Or finally, I could just walk up to this big guy and smack him really hard for a lot of damage assuming I hit, but I don't have combat advantage against him. Oh wait, Tim did you want a save? Because if you do, I can choose this fourth option."
Then invariably, you get somebody who 5 minutes after their turn is over "Oh, I forgot, that ogre I hit, should have taken 2 extra damage because of (insert reason here)"
Don't get me wrong, I still love 4ed, and its the only edition I'm playing, but it can be frustrating both for certain players, and for DM's or other players who are gaming with the more tactically minded players.