Building on what Richard just said,
Working on a distro and being supported on a distro are two different things. LC does indeed work on many "unsupported" distros, but the ROI for actually supporting a wide matrix is pretty small, especially considering how small the revenue stream from the linux build probably is. In order to support a version you have to make sure that new additions and bug fixes work across all the builds, you have to deal with tech support issues, you have to test each build as it's built... I've done QA work before where we had to run through the gamut of tests across a couple of dozen combinations of browsers and operating systems, and it's a *lot* of work.1. Getting "the thing" to work on the vast majority of Linux varieties.
By limiting the distros that are officially supported (mine isn't one of them) LC as a company can commit to fully testing and declaring functionality across the most popular major distros, while also saying that other distros may well work, they just aren't part of the test matrix and if they don't work, they don't. I actually haven't come across any distros that wouldn't support LC, so I'd be interested in that list.