So have you noticed that since 3E on up UNLESS you had a Character Builder of some sort that NPCs were hard to make?
Even if you made them in 3E that would be cumbersome to run and ever more so in 4th edition.
Notice from 2E on down that a huge party of PCs and NPCs were easy to make and run? I mean I use NPCs as cannon fodder to keep the heroes alive. Not a problem when you can make one up in less that a minute. Just try running a party of 8-10 players with 12 or so NPCs in the 3rd or 4th edition. It works in 3rd edition BUT they will have full stats IF you use the rules as written. If not they will be massive unskilled retards. God I would not even have enough room on my table for a 4th edition game of this sort.
Now for something completely different!
With the 4th edition the age of the Megadungon is over for the modern gamer. Just go and try and make one. I already have for LL/S&W. You go make one for 4th edition with at least 100 rooms per level. See you in a 100 years. We of the OSR shall enjoy the mysteries of the huge Megadungeon!