If every subscription app runs on an external server, then I get it. For 3 years, I paid over $30k to have a gallery in a hi end mall, and made nice profit every year. So I understand the cost of doing business and that some of these apps may be worth it. It just seems like many could be, or are, one-time installs. I could be wrong.
As an example, there is a competing app to MagicZoom that keeps images on their server rather than just using the product images. MagicZoom is $79 one time. The other is $45 - $465/month.
It's just my customer input for the developers. If you are able to make the app so you can sell outright, I am more likely to purchase.