Why proprietary software is all wrong

It's not that I don't like individual proprietary software, it's that I don't like it in principle.

A case in point is Axure, the wireframe and prototyping software. I've been playing with a trial version because I would like to create a web application to do a similar thing. But on running the software for the first time, this message came up:

“Files created in version 5.6 will not open in versions prior to 5.5. Colleagues you share files with may need to purchase a renewal.”

There we go. Users being forced to upgrade to ensure compatibility. Isn't that all wrong?