Obviously I can appreciate the fact that time and effort goes into developing and maintaining your modules. But I also think when people buy a product as a one time purchase they expect the vender to honor his agreement. I buy themes and software all the time, some of which are one time purchases and others involve renewal fees. But I know the terms before I purchase and make my decisions accordingly.
With all due respect, I think what you did here was wrong and bad business.
The issue here isn’t whether or not you “sent out notices” or that the cost is now only a modest 10$ extra per module per year. The issue is that these are not the terms I purchased under, and for you to hold your early customers hostage by suddenly demanding yearly fees … I’m sorry that just isn’t right.
Not the end of the world – but I did feel the need to express my opinion. I am only thankful I didn’t purchase more modules when I initially choose to use this product.