Where do you think they make the most money?

People like you that want to just buy the software upgrade and do it themselves

or

From companies that bulk purchase licenses and sell millions of computers with the O/S already installed to people that want to update.

If you picked B you're right. Which explains why upgrading is frustrating to you and is causing you to think of buying a new computer. That is exactly what Microsoft and its trade partners want.

Windows 7, I could pontificate - but I've got a Mac!

I installed Win 7 on my second partition.  Not sure what all the fuss is about, really.  It's just a slightly different looking Windows, especially if you revert, as I always do, to the classic Windows appearance.  And some of my applications don't work, such as my anti-virus software.  I bought it at the discounted £44 rate but I don't think I'd pay any more than that for it.  Certainly not the £150 now!
If you have a large disk drive and Windows XP already installed then the Home Premium (supposedly an upgrade) can be installed separately.  You just download a free partition too (like GPart), create your partitions, and then select the custom install from the CD/DVD which runs on Windows XP to install on the new partition.  Then, you get a dual boot menu when the PC starts up.  As the file systems are the same, both partitions are visible from either version so copying files is just a normal file copy.  The install was very very easy, and quite quick.

You lost me after "I" at the start Daniel

Real, having FREE SPACE on your drive does not necessarily mean partitions. Generally speaking you always need some free space for your computer to work.

My Win 7 installation is ~17GB.

17GB! And to think we were wachling about with a few K, when home computing first came on the scene.