STL files stand for stereolithography files. Those files are mainly used to represent manufacturing 3D objects. This is why this format mainly contain the surface geometry data which is different from others formats who also take up textures, luminosity and others informations.
In September 2013 they've released a diff visualizer for these 3D STL files. This is a very cool feature easing collaborative 3D model design and improvements. Looks like it's working using BSP Tree comparisons but you can check it on the Blog post.
Hope those features will help people in their 3D modeling so they can release them for the entire world.