Poser 8 brought Indirect Lighting, new library system, improved rendertimes, new user interface, new figures, new rigging system and multiple falloff zones for joints, morphing tool can be used over multiple bodyparts, dependent parameters, inverse square falloff for lights, better plugin support, tone mapping, better OpenGL support and other improvements. All features requested by the community for a long time.
This is a major new version of Poser and much more than a glorified service release.

Poser 1 and 2 were released by Fractal Design in the 90s. It did not even include transparency support and was no more than a tool for (hand) drawing. It still can be used as such, but has grown into much more when it added animation, figure rigging and much more realistic rendering,

When I bought Poser 4 Pro - which some mention as the most stable release of Poser - I deinstalled it after a few weeks and went back to Poser 4 because it trashed my saved files continuously. Poser 4 never had that problem. Half a year later I bought a new PC and tried Poser 4 Pro again and never had any problems of this kind at all anymore. Was it a problem with Poser or with my old machine?
I really have no idea.