It's a pretty good chunk, but not nearly all.
One of my favorite things to do when a new set comes out is to take the Monster Manual off the shelf, flip through it from front to back, and note how many of them are actually minis nowadays. There are lots of them, but there are also significant gaps (most notably the rust monster, as discussed on another thread).
It seems like every set adds another two or three monsters from the Monster Manual, but they also retread alot of the same territory over and over again so that common monsters (such as orcs, hobgoblins, skeletons, ey cetera) are available to newer players. I don't even mind that, because my goblin horde is now impressively large.