There should be a lxs file when distributing a test scene or preview scene. Granted most are using Blender for their freebee tool of choice. However, many use other tools and would look to LuxRender in a capacity no different then say a Maxwell, Indigo, Octane, etc. The mere fact that the lux boys are distributing test scenes/preview scenes only in Blender using the good 'ole LuxBlend plugin as the defacto interface to LuxRender limits your target audience. After all LuxRender folks have to be cognizant of the overall penetration of LuxRender in a very crowded market of PBRs.
Don't get me wrong, I'm a huge LuxRender fan and writing a fully qualified Houdini exporter, IPR, materials editor. Of which I chose lux over Indigo or Octane to write this exporter/plugin for Houdini.
Just my two cents worth and some advice being active in CGI and the market, stick with releasing both blend files and lxs files so that you can support both your mainstream fanboys as well as support your native format. Any veering away from your native format sends a clear message to the community and others that you are merely targeting Blender as your primary platform interface of choice. Not a good thing to do in the long run.
Just some experienced advice