Deepbit had controlling share in the network a couple of times and we survived. They won't do anything because it's in their best interest to play nice. Think about it a minute. They're holding a mass of btc profit from running a successful pool. They could continue making more money but instead they decide to make their holdings worthless by fucking with the network. Yeah, that makes sense. Calm down people, the sky isn't falling.
Their "mass of BTC profit" isn't from their pool. Their pool costs them money, it makes them nothing. It has, from day 1, made absolutely no economic sense for their pool to exist at all. Their private farm is as large or larger than any other pool as is, so the argument of letting others join them to reduce their variance is moot. They're too large for variance to make an impact on their monthly revenues. They're paying to run servers for people for nothing, unless they're skimming from the top.