"Support for what exactly? Most common PC hardware works out of the box."
Talk to performance gamers. High-end graphics support tends to lag in the Linux front, which kind of puts a crimp on Valve's effort to push Linux gaming with Steam Machines. Flaky graphics support is one reason I had to abandon Xubuntu (spontaneous resets), and my Radeon 6850 should've been near the top of the support list.
"IMHO hardware support under Linux is far superior than any other OS."
Oh? I tried Ubuntu on a old Dell Inspiron. Fell flat because no nVidia driver worked on it. Noveaux was too slow and the nVidia blob wouldn't support the chipset. Dead end. And this isn't the first time.
"Linux is a kernel. It's not really the kernel's fault that the current desktop market share is mostly Windows so that's what commercial developers target. There's nothing particular about the Linux kernel that means the type of applications that run on Windows couldn't run on Linux."
But the Linux community, which includes the kernel community, should be pushing for most mainstream support, but they're not, so they're in the rut they are now.
"So you're not talking about Linux. You're talking about common types of applications that desktop users need whether they are running Linux, OSX,... Anyhow this is going to be less and less of a problem now that everyone wants to use more portable development tools etc so they can get their stuff running on the desktop, web, mobile etc."
Except the desktop will continue to exist for performance applications like gaming. See the above common beef PC gamers have concerning their video cards.