Most of the 'high end apps' seem to have a large number of plugins avialable to extend or optimize their functionality. Extensibility is also an important feature. In film production at least,  I don't think I've read about a feature film that used stock Maya for instance - it's always customized to their way of working, and they often create new tools and techniques for each film. In addition to functionality and customization, you're also paying for speed and stability.  You can't be having your s**t crashing in the middle of a production. They also don't rely on a single application. You might have Maya, Max, Vue, RealFlow etc. all used on one production - whatever tool works best for a particular need.  That means your app has to play well with others.

Poser scores better on some of those than others. I think that for many people, it's reached a point where it meets their needs for stills and animation and they really don't need anything 'higher.'

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken