I think it is much worse than the issue of charging more and/or additional for the same product bought under a clear agreement and understanding.
For those of us choosing to maintain version 4, there would, at this time anyway, seem to be zero support. I have a number of issues some of which are extremely serious and damaging to my business that are being ignored. In fact one of the statements from a so called 'support engineer' was "This looks like a defect on this version, please backup your system and roll to 4.5.1 or version 5, unfortunately I cannot test 4.6 since that was an overlap version to 4.5. , our development team are only working on V5 today."
So, the question is, even if we bought into the very expensive upgrade, why would we be inclined to believe that the next major move on this prouduct would not leave us as high and dry as this one. Version 6 could as easily come with the same kind of price hike, and be forced due to no version 5 support.
A class action springs to mind folks?