I understand drawing a line, I don't mean to say I don't understand that, but not even a 3 month window for new purchases?? As far as customer morale so to speak, I am sure it doesn't give any of your newer clients much in the way of warm fuzzies.
So I am not saying that you don't have to draw a line, I am just saying that in some ways making the choice to narrow that window so short, isn't being very considerate to your newer clients. Look around at the software industry, most at least give you 6mos or a year of updates when you buy a product new. Heck I have quite a few products that I pay up for every year to support them, but I know when I do, that I get a year of updates/upgrades for that price. In short, and in many ways your punishing your new purchasers (unless the purchase was super recent), but for old clients that had prior versions the update is an OK deal.
If I had the package for a year, maybe two, or three, I can update for your set fee and life is good and fair. If I bought in a 2 month window again I get current stuff. If I am the unlucky patron (as I am) that purchased the software a lil over 2 months ago, well tough luck bud, as you bought it at the wrong time. Heck even some pro-rata on it would be something. Again I am not going to loose any sleep over $20, but having purchased lots of software over the years, with many on upgrade/maintnance plans, I am just saying your really doing your clients like me, who are recent purchasers, a huge disservice with how you have this all structured. I may very well be talking to the wind, but you really should consider how your making your clients that bought your product feel that paid full price for it all of 3 or 4 months ago, as your really overall shutting us out..
Regards...