Well -- that ratio of systems to users to supportive personal is 1:2:1 in your house. That ratio is incredible, give me a company of 50 people with 25 PCs and 25 IT people and I could get them running on nearly anything.
Now, start over and format your mothers computer hand her a Linux disk and refuse to help -- now you have a better idea what the "average" user would experience.
I agree with you regarding the support ratio but disagree with you that Windows is necessarily easier to install on a blank machine.
I think that an uninformed user would probably struggle just as much with a blank computer and a Windows install disk as a blank computer and a Linux install disk. In fact, I'd argue that right now some distributions of Linux may even have the advantage since it gets used in that context far more often (most people have Windows pre-installed).
I suspect we may need a scientific test to know for sure.
But a user that's a tiny bit above average can (I hope) probably google around to find a screencast or article about how to isntall Windows XP, Vista, 7 or 8. It's a million times easier, because the options are limited (just a few Windows versions are around).
On the other hand, we have millions of Linux distros, with folks like Ubuntu giving out new versions on a quarterly basis and often change, move or tweak small things in the installation panels which makes it very hard for the non-geek user to install, say, 12.04 if they're watching a YouTube video about how to install Ubuntu 11.10.
I absolutely hate Windows, but sadly it's much more user friendly than Linux. Thankfully, OS X is still around.
Now, start over and format your mothers computer hand her a Linux disk and refuse to help -- now you have a better idea what the "average" user would experience.