The Diablo III Impact on World of Warcraft

I'm not sure that Diablo III will feature the same hooks or cater to the exact same audience as World of Warcraft does, so I find myself agreeing with the gist of this new editorial on Ten Ton Hammer that downplays the impact the release of the former will have on the continued success of the latter. However, that doesn't meant that I think $15/month is a "drop in the bucket", as the author does:
I know what you're thinking: won't players drop WoW to get rid of the 14.99 subscription fee? I've thought long and hard about this and I just don't think this will happen with the grand majority of players. 14.99 a month (as long as you are paying for one account) is really a drop in the bucket for most of us, I don't even plan on cancelling my THREE subscriptions just because Diablo III is being released. It just doesn't make sense.

To further cement this fact keep in mind that WoW and Diablo are totally different games. While they are created by the same company the similarities (if D3 turns out to be much like its predecessors) will be minimal. So why choose just one when you can get two vastly different play experiences for the same subscription fee that you were already paying? Because the two games are bound to be different, and I stand to be corrected if this turns out to be untrue, and as long as your love affair with WoW is still strong, there is no reason to choose one game over the other.