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.