On a serious note, I've only been a player in 4e and have never DMed it. But my assumption based off of my experience seeing my options as a player would be that a big reason creating an NPC in 4e is easier is because there are way less options for a 4e character than there are in 3e. Is there any truth in that? Is that what people are talking about when they say 4e is easier to manage? Or is character creation easier for another reason?
The big reason creating NPCs in 4e is easier is because NPCs and monsters are not built with the same mechanics as PCs. It was an experiment of 3e to build all monsters and NPCs with the same rules of creation and advancement as PCs. It was not a part of the game before 3e, and was not continued after 3e. In 4e, monsters and NPCs again have their own creation rules which stress their different roles within the game. A player wants options and expects to spend some time creating a character. Making the DM apply that same breadth of options and time expenditure to create every monster and NPC in the game is going to slow him down. He has a much bigger cast to worry about.
What's interesting is that 3e is the aberrant edition here, not 4e. It's options took characters well away from the core D&D principle of archetypal classes (or races). Many people like this and I am not attacking 3e as bad for it, just as different than all other versions of D&D, including 4e.
In all other versions you pick a class (or a multiclass combo, or a race) and that's what you are, even if you multiclass. The answer to the question "what are you playing?" is "fighter" or "elf" or "fighter/thief". It's a recognizable archetype of D&D in a way that barbarian1/scout2/fighter2/assassin3/shadowdancer2/ninja4 absolutely isn't. The mix and match character design of 3e suggests that a classless version of D&D was almost presented, but the designers didn't want to sacrifice that particular sacred cow. Now, many players of 3e did not like examples like the above and houseruled limitations, demanded players pick a class and not level dip just for class abilities and so on. That's a houserule, though. The system was designed just for that sort of thing. If your goal, starting out a character, was to play a Wizard, the archetype and the class, then you didn't have an amazing set of options, you had some feats and a prestige class to pick that enhanced your wizardliness. The abundance of choice only really came into play when you approached creation as in the example above, well outside the idea of classic class-based archetypes.
Again, if you like that sort of thing, that's fine. But within the context of specifically D&D, 3e was the only time this style of character creating (and NPC/monster creating) was attempted.