The other scenario is that keeping prices reasonable means there isn't as much demand for an open source version. Developers who balked at paying $150 a seat wouldn't be sufficiently motivated if the cost was a more "reasonable" $20 say.

I just remembered a pretty good example of this with the story of BitKeeper and Git, you can read http://kerneltrap.org/node/4966 for more information. It was the catalyst of losing the cheap enough/free option that motivated the work on Git.