Email has too much momentum to ignore? See Facebook's messaging - they're happy to ignore and cut off email. If they get away with it, it's a huge win. If it looks like they're not gonna get away with it, then they reverse decision and talk about opening up or whatnot.

I don't believe that it's clear at all that Google, FB, or Skype would win by opening up their systems. The best we're likely to see is alliances, like FB+Skype. Unless a service is in a losing position (like BBM), what do they gain?