I think the point is that the bugs are being fixed in a new paid release, and not in the release many people paid for.

The only thing, imo, that this does is harm the relationship between people developing software who would like to be paid for it and their customers. If you charge people money for something it behooves you to keep releasing fixes and point releases for it regularly, not to disappear and release a paid upgrade with the things fixed that should be part of the current release. I don't know of any legal or moral obligation to do it, but it certainly is a good business move for the ecosystem.