Has anyone given feedback to Mathematica about specific STL files that don't mesh well? I am in contact with a technical person at the moment, and it seems like they have not really heard from 3D printers. If they get a lot of comments of specific code that does not produce a good mesh, maybe they will really try to improve their STL output.
At some point last year I wrote an email about a few issues and never heard back. My was frustrating me was that Graphics3D Tubes were not solid when exported. They lacked end caps, and the joints between tubes were missing the elbows on one side and overlapped on the other. Its especially frustrating given the potential to directly export to ZPR format in color for 3D printing on ZCorp machines. Clearly they had 3d printing in mind.