All of the big CAD packages (Solidworks, CATIA, Solid Edge, Pro-Engineer, Rhino, SpaceClaim, ...) are Windows only. Lately OSX has gotten some traction, but it's still pretty marginal.

There are translators (e.g. SolidWorks -> STEP, SolidWorks -> STL) that run on Linux, but the better ones, and the ones that support the proprietary formats (SolidWorks, CATIA, etc.) all cost money and couldn't be included in a Linux distro's software repository.

So even if Linux supported 3D printing out of the box, it wouldn't be as useful as if Windows did, IMO.