Let's see it this way, how many people have Macs vs PC, 5-6%? How many of those play games on their Mac, 5%? How many of those are eventually playing WOW, 5-10%? Like potentially 0.0125 person per 100 Mac owners potentially playing WOW. So you need 8000 Mac owners to have one playing WOW.
Even if on Windows the WOW player base percentage is not greater, the machine count is 19 times bigger, so potentially for PC you may have 19 WOW players vs 1 on the Mac (and I am sure the ratio is a lot bigger than that).
Now, knowing how money greedy Activision is, you can imagine that developers spend a lot more resources on developing Windows WOW vs Mac WOW. Plus for sure most resources are currently oriented towards developing new games vs maintaining old ones.
I'm not saying that the Mac WOW developers are not dedicated to their work, just that they are not given the resources to do a good job.
Just look at the fact that Call of Duty WAW 2 is not even released on the Mac yet, that proves how much general interest there is for investing in Mac gaming.
With Windows and console gaming, MS and hardware manufacturers give $$$ to help develop the games to support their own sales, I don't think Apple is helping out any gaming studio with $$$ right now. They are interested in gaming on iPod and iPhone.