I don't think the pro-audio/pro-video market are really that big a market, at least not compared to the amount of consumers they could pick up if they dumbed down the OS. Especially given that for the most part, pro-audio people and pro-video people spend a heck of a lot more on everything but their computers, compared to their computers, and in growing number have specific needs for their specific workflows that probably add to Apple's support and development costs. It's likely much easier to sell Grandma and Grandpa a simple e-mail and video chat device, and then support them with low paid scripted employees, than it is to make sure that the Firewire chipsets are as low latency as possible, or ensure that there are no problems installing the hard drives Native Instruments and East-West sell their sample libraries on now.
I mean, for every pedantic professional who needs everything to work just right all the time that you lose, if you can grab like, 3 or 4 consumers on lower end machines, you're probably making MORE profit. Especially on stuff like Applecare, etc.
I also don't see it really hurting their education sales much if they go really consumption based. In fact, the easier it is to just lock down the devices, and provide simple apps, the more attractive you've made the devices to the K-12 market. Downsize your sys-admins, buy Applecare for everything, and really, what problems will you run into with a glorified iPad in K-12? There are even benefits. Less risk of some kid knowing more than the under-paid sys-admin/english teacher and exploiting a hole, screwing around with "expensive school resources".
It's short term thinking, sure. But that's fine in the eyes of most stock-holders, so what does it matter?