Every time this speed comparison between Linux and Windows is done, it is done on newly installed systems. My experience is that after six months of running by a regular (read non technical) user, the windows system will be bogged down by all kinds of crap that make it unbearably slow.
So, "don't install crap" is now a technical skill? Wow.
My wife his hardly technical, and I haven't had to touch her laptop since I installed the OS on it. And her laptop moves along just fine. Faster than mine, in fact, but I can blame that on the oddly matched hardware I've got.
I tell you what -- setup a linux install for your "non-technical users", give them the root password, and leave them alone for six months. Assuming they don't find a new techie who will let them actually play games on their machine, I'll be they'll wind up every bit as bogged down as as similarly-configured and abandoned windows installation.
Or, you could realize that installing programs is an admin function, that a properly installed program doesn't force a user to run as administrator, and fix the problem on the front end. Hell, you could even post a sticker that says "DO NOT INSTALL ANYTHING" if you want.
Oh, and show me a netbook with a comfortable keyboard, and you'll have a no-brainer. I can't find anyone who can stand the damn things.