The issue isn't with the similarity in purpose/capability, its the difference in market.

Its the same with everything else you have mentioned. The average Poser user would not even attempt a Re-rig of a commercial figure. If you buy a figure for $50 you would expect if to be fully functional in the intended app and not requiring any additional work to reach expected or stated levels of functionality. The intended market for the other apps is more aimed at the content creator market not at the ready to render market.

A reflex hammer and Sledge hammer are both hammers but intended for different uses and different markets.