"All built in to the distro" is a bit misleading, leaving aside the fact that a large portion of Linux drivers for consumer appliances are junk. Something as trivial as getting 3D graphics support on an AMD card was a drawn out command line process on Mint when I tried it last.
Don't forget that most people that say "I only need web and email", actually mean "I only need a browser, email, image editing software, ability to connect my digital camera, printer, scanner, share printer on network with other windows machine" etc etc.
It's possible to get OSX running if you pick your hardware carefully, I've got a VM running it.
Driver support. So, what you're saying is, because driver manufacturers provide simple GUI based installation routines for Windows, and not for Linux, installation of 3D graphics on Linux is more difficult. Quelle Supris. Actually, it's suprising that you get 3D drivers for Linux at all. Nvidia were (not sure if they still are) pretty good with driver support (although last time I bothered, you still had to compile the drivers yourself), whereas AMD based drivers were more or less non existant.
That said, when I last tried, I got better framerates on older hardware and cards running Linux & linux ports of RTCW (showing how loong ago it was) than under Windows.
But that said, it's horses for courses.
Linux is great in the data centre (I really wish the Windows boxes I have to support were Linux, so much less downtime for patching).
Linux could be really good for non power users to use as a desktop. Whilst I prefer Debian, I thought I would give Ubuntu 12.04 (so not even the current version) a go on an old EEEPC900 (early notebook) just to see how it's progressed.
Browser - Tick
Email - Tick
Image editing - Tick (the gimp / image magick) - The only reason you don't get Photoshop is that Adobe don't see the market. It wouldn't be that difficult to port the *nix based OSX code to Linux if they wanted to.
Connecting Camera - Well, it reads SD cards, which is exactly how I read the card off my camera. Can't see an issue here.
Printer - Didn't bother, but CUPS always used to do a good job, I'd be suprised if it wasn't better than I remember.
Connection to other Machines - Yup, told it the address of my NAS and credentials. Bosh, straight in.
Huawei Modem. - Blimey, that was a Tick too. Really wasn't expecting that.
Office Software - Came with something that read / wrote docs and xls okay, plus Open Office is out there if you want it.
Gaming is the next biggy to crack. Sure, as I said, you can do it, but really, you currently wouldn't want Linux as your gaming rig of choice. Limited availability, and yes, 3D drivers are not yet out of the box.
But Steam OS will change that.
Don't forget, Windows has a 9 years head start on Linux, and had the might of IBM & VMS programmers working on it (OS/2s code, and MS obtained VMS programmers when producing WNT) - Windows has always been a comercial affair, Linux spent the first couple of years as an experiment in usenet land, you probably wouldn't have wanted to play with it unless you were a coder, until 98 at the earliest. It's amazing how much it has come on, and really, quite shocking that Windows hasn't disappeared off into the distance.
Would I say people should all switch to Linux. Absolutely not.
Would I say that I can see a market share where people could. Absolutely.
For instance, I (and I'm sure most techies) already end up as unpaid Tech Support for parents / grandparents / friends, who really only use their machines for email/browser/camera/skype/java games etc. I loose count of the amount of times I've had to use an RDP session to fix something remotely.
Give them a non root account on a linux desktop, with automatic updates, and I bet I would be fixing less, and when I did have to, I would probably just ssh in and run a terminal session, maybe xforwarding to my desktop. Can't see that it would be any harder, probably actually easier.