Thing is, for Windows it is true. An average user can install Windows, feed in the disks for each of their peripherals one at a time and use the GUI to install drivers, connect to their ADSL modem using the helpful CD with a Windows-based setup script, and be on their way.
Perhaps the "average users" that you've seen have possessed more knowledge than the ones I've seen. I have never, ever seen someone manage to go from a RTM XP disk to a fully-configured, fully-setup install with 100% functional hardware unless they were quite knowledgeable w/ regard to Windows administration.
For Linux, a lot of the people who make the software/drivers you use can't see an advantage to being able to do everything through a GUI.
Not true at all. I've been using *nix (in some form or another) for almost 15 years now. I'm quite familiar with command line usage, but I prefer a GUI for a lot of things -- some information is better presented in GUI form, and package names/descriptions are (in my opinion) some of those pieces of information.
There might be a GUI that works most of the time, but that's not good enough: take package management. It's fine until you hit a problem it can't deal with, and then you have to drop down to running the dpkg stuff manually to sort it out. That's why I won't recommend Linux to any non-techie at the moment, as "Works with a GUI 95% of the time" is not enough.
Oh come on now. At this point you're basically saying "Yes, there is a good GUI -- but you might run into something you can't solve with point and click!" Well... yes. That's the case for every desktop OS out there.
I could say the same about OS X, actually. OS X is great, unless you need to flush your DNS cache, and then you have to drop down to running the dscacheutil stuff manually to sort it out. That's why I won't recommend... etc.
The command line isn't some great evil -- it's a powerful tool, but it's one that's mostly unnecessary on modern Windows, Linux and Mac OS X desktops. From time to time, be it for troubleshooting or setup purposes, some folks may need access to it -- but by and large, on all three systems the average user does not. I really don't get this whole "the command line is sacred and must never be needed by anyone ever" thing... Sure, you shouldn't need it for daily tasks, but not all problems can be solved with a fancy GUI. Objecting to the use of an OS on the basis that there might, at some point, be something that someone can't handle by clicking a button is silly.