I can only assume they think this way is how they will get most money from selling to end users, and I wouldn't be surprised at that being the case. No doubt they make most of window's licence money from OEMs.
I can't use Chevy parts in my Honda, but if Chevy started charging 1/10th of what Honda is charging for similar parts, Honda would need to lower prices if they wanted me to stick with them for my next car, or to use genuine Honda parts instead of third party parts to repair my current Honda. That's because Chevy's price would help recalibrate my expectation as to what kind of prices are reasonable, making Honda look overpriced.
OSes aren't as interchangeable as cars, but a Microsoft upgrade price significantly higher than Apple's upgrade price might convince more people to stick with what they have until it is time to buy a new PC and get Windows 8 bundled, rather than buying an upgrade, because Apple's prices lower the expectation of what an OS upgrade should cost.
And your forced car analogy is seriously flawed.
I find it very hard to believe that MS hasn't had a good look at Apple's OS X pricing strategy before making this move. It mightn't be that they feel pressured into lowering the price so much as they've just seen what Apple has done and think it's a good idea to get as many people to upgrade as possible.
*912, 914, 924, and first generation 944 parts sourced from VW excepted.
For many people, changing OS is probably similar to learning manual when they're happy driving automatic.
The old options was buy a lower priced computer with Windows but pay more for the OS/upgrades or buy a very expensive Apple computer but $40.00 for an OS upgrade.
e.g. http://www.wired.com/gamelife/2006/11/isupply_ps3_com/ ~ costs the PS3 components at $850 vrs the $599 retail price.
As for this topic: I don't think it's aimed at consumers, at all. Many companies still use XP as their back-bone, let alone 7. It's aimed at the software producers, akin to why some games companies are developing purely in DX11 now to reduce costs having to support DX9 ~ MS are making a switch to producing content for W8 as 'attractive' as possible.
> you can only install it on Macs (which already have OS X installed).
It wasn't an attempt to compare OS X and Windows installations.
- Install Windows retail SKU, but do not activate it. You can borrow disk or download ISO for this. - Start installing upgrade version, then reformat partition, supplying upgrade key in the process.
At the end, you will have Windows upgrade installed and activated, fully functional.
For Windows 7, if you have machine with empty disk, then you start installation of upgrade version, but do not provide product key and uncheck 'Activate' checkbox. This will install Windows in trial mode. Then, start upgrade setup again and let it 'upgrade' OS... After that, you have activated Windows on the machine.
For Windows 8, I am not sure if process of double installation will work.