Issues around permanent licences

I was thinking about getting Fences 6, having used a much earlier version of Fences some years ago. However, I decided not to proceed, because the upgrading situation appears totally unfair, inasmuch as one could purchase a licence, only to find a few days later that a new version had been released and not be eligible to upgrade to the newer version. A much fairer option would be to allow upgrades for a set period of time (e.g., 12 months). What do others think?