Or use "The Dutch Model":
replyPay for the major version, get all of its updates. Then pay for update (to next major plus its updates) with a discount.
If you don't prefer the pay, you can keep what you have.
This is what Reaper, Forklift, CameraBag and countless others do, and it works very well.
Edit: This comment contained Forklift as an example before, but they have changed their model, so it's removed.
Forklift only sells you a year of updates at a time now.
replyYeah, you're right. I remembered it now. However, they have stopped doing "major" releases at the same time, too.
replyLet me update the comment.