This is something Marxists learned to take advantage of in the latter half of the 20th Century, Whenever and wherever there was social unrest, the communists almost always came out on top. They learned that when there is upheaval, most organizations and coalitions are only loosely knit. There exists lots of confusion and people instinctively look for order and an authority to turn to. The Marxists are always prepared for this, and always stand up at the key moment and announce that they are in charge and everyone can relax now. It then goes downhill from there.
Marxists learned this in the first years of the 20th century. Lenin wrote a whole library of books on the technology of revolution, and he was largely correct. His methods are still in use because they work.
With regard to the "grassroots", I don't believe it for a moment. Revolutions are dangerous things, nobody would participate in them just out of the blue without a good reason. And I don't see why Egyptians would suddenly, all at once, find such a reason last week. Egypt is stable, reasonably safe, and more prosperous than many any of its West African neighbors. There must be a leading force behind all of that, and the revolution is unfolding exactly as they planned it. People and governments are just pawns, they don't have time to think, they aren't trained for counter-revolutionary activities, and they don't see the whole picture. It usually takes a genius to turn the tables on revolutionaries.
Good observation.
Cuba comes to mind...and Castro.