I know that Apple has their policy because they believe the software is more stable on their platform and because their profit strategy works better that way. MS, OTOH, I think, wants to damage Apple, as it has gone from being a minor pain to being a genuine concern. MS has always believed that the best computer strategy is the strategy of the Borg. I think they also fear people getting used to having another OS, and liking it better.
I honestly don't think this licensing restriction has anything to do with Macs. Just as with XP, they want to charge more for the versions that have greater functionality.
I was trying out a new piece of software a few months back on a spare laptop, and as part of the test I needed to share a SQL database over a network. But I couldn't do it on that laptop because it ran XP Home, and on the network component of the software required XP Pro.
Similarly, virtualization isn't yet something most casual or home users run. Those who do want or need that technology are expected to "step up" to a more advanced version - those capabilities are the reason they have different levels of the OS at different price points. Sometime this year I'm looking to deploy a server running several virtual machines, none of which need to do anything very fancy. OSX and Linux aren't options, so it's a case of MS getting to charge me an extra $100 per VM because the Vista version that runs in a VM costs an extra $100 over the version that doesn't (or isn't licensed to).*
I just wanted to point out the silliness of Mac lovers getting up in arms about some (IMO nonexistent) conspiracy to charge them more, when Apple doesn't permit the same functionality to PC users at any price.
*-Actually the plan is to buy a stack of XP Pro licenses from eBay or somewhere, because I don't want to migrate. But the point is the same.