Its a psychological number, the main strength of bitcoin is to be a decentralized system, is now more and more concentrated by a single entity. It shall make headlines!
I honestly thought that miners, with all they have invested and have to have invested these days would not be so stupid as to let this come about. Maybe it's time to diversify a little.
I think the problem (not really a problem) is that mining has become dead-easy (it must be if I am) and mining hardware is really easy to come by, so there are a lot of people getting into it that don't really know a lot about bitcoin and they go straight to the biggest pool that offers the most reward. As I mentioned, it happened a few months ago and once word went around people left in droves. I guess in the end it's a good way of educating newcomers to the game.
People will mine at GHash.io, just like people will order hardware from bfl, there's always fresh meat.