WoW's fluctuating subscriber numbers reflect the natural state of a 7 year old game that is in a down period between expansions, so I'm not worried about that. Instead what I think is going on is that they've spent so much time growing their staff to accommodate WoW, the new Battle.net and new projects like Diablo 3 and the unannounced MMO project that they've come to a point where they've decided to take a good hard look at who's working for them, how they can optimise their workforce, and how they can cut down on the bloat.
It's likely a matter of reducing overhead and improving internal communications as opposed to any "bad news" that they need to get rid of people in order to keep the ship afloat.
As the CEO says, this is something that happens when you grow a lot: you need to make some changes every now and then. Instead of viewing this as a cutback, I'd view this as a fundamental step towards stabilising themselves as a developer that handles multiple projects simultaneously, whereas before they really operated in serial.
Taking 600 off the top of 4700 employees still leaves them with over 4000 people working for them, which is about as many as Nintendo employs, to give you an idea of what kind of sizes we're talking about in the games industry.