Consider the following...

The original idea of this subscription model (MMORPG model) is that expansions and the like are free because they are paid for by the on-going, monthly income. However, some games couldn't keep good to that because they didn't get enough success or had to pay back huge advances, etc. Is blizzard in this situation?

10 million (users) * 12.99 (the cheapest subscription option) * 12 (months)

This is equal to a gross revenue of just over 1.5 billion dollars a year. They, more than anyone, can afford to do expansions. Granted, we don't know the operating costs they have, but still...1.5b is a big number. These days, starting from scratch and building a AAA next-gen title runs you somewhere between 10m -100m. We're not even talking about that though...we're just talking about an expansion.

Are you at least a little burned up about having to buy burning crusade and future expansions? I'll be first in line for the next expansion...but I'm still a little irked about buying what I already funded.