"Linux is actually about 5,000 different distros with all manner of combination of library versions, etc. Shipping an executable binary for "Linux" is exceedingly difficult as you have to have 20 or 30 different version for different distros (if you say, we support RHEL 5, then you get a bunch of Gentoo goobers whining).
Linux is also really lacking print drivers, video drivers, etc., and for things outside of servers, is just FAR FAR behind other platforms in terms of technology and in terms of market share."
I can name several companies that manage this fine, basically you just have to be careful with your build machine. You'll notice that VMWare ship a single Linux installer for VMWare Workstation and that works out of the box (ignoring the kernel modules, which Lightroom won't need and is a vmware special case).
Also there is a very large gap between "supports" and "works on". I have no problem with Lightroom being "supported" on Ubuntu Feisty or RHEL 5 or something else, just let me install it on any Linux and if it works, I win. If it doesn't, tell me to install a supported distribution.
Regarding video drivers, that's just wrong. Linux has had 2D and 3D acceleration for a long time, with fast drivers being written by Intel, nVidia and ATI.
Regarding printing, LPR is the classic printing interface dating back to primordial Unix times. CUPS has managed to take a huge percentage of the printing service area that I can't think of any distributions which still use LPR over CUPS by default.
Yes, Linux is way behind Windows in market share. Then again, so is OS X. :) Linux is growing massively and there is demand for industrial-grade applications like Lightroom, see the amount of work on GIMP, Bibble and so on. A favourite argument of mine when people say that nobody professional uses Linux is to point out that both Dreamworks and Pixar use Linux for the creation and rendering of their animated movies.