I've bought 3 different versions of Parallels, all of them within a month or two of a new version which I had no idea was coming, and all of which then required me to pay again for the new version. My favorite was the one I bought literally the night before the next one was released. No love from Parallels on that one either.
I realize we can't always expect a company to offer upgrades for free, but this is the only one where I've had it happen this many times, and have gotten no concessions.
Thank you