The 'save' and 'export' functions were differentiated to make it clear that data is lost with formats other than the ArtRage Painting (ptg) file format.
The alternative is to pop up a warning that saving in certain formats loses information, but that can be a break to workflow as well.
While many of the users of ArtRage are professional users, many other users are very new to digital painting and may not appreciate the importance of saving and loading projects in their native ptg format.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"