It's not in their interest to provide players with one more reason to quit the game for the sake of making a fraction of their total revenue for greed.
They will have a much healthier, long term player base if they bite the bullet and realize that this was a feature a lot players have asked for for so long rather than to tack on a price and expect the community to bite. If anything, the community is already strongly against this but due to massive censorship on their forums, threads will be squashed before they are read.
Right now, they risk losing subscriptions which not only lowers the potential for that extra income but also the flat $15 which the entire structure of this game relies on. While premium services will go to line their pockets, the base subscription fee is what allows Blizzard to maintain their hardware and such.
This is not only a problem now but a future problem as well. Think of the implications this may have on Diablo III or future Blizzard games.