Their answer would probably be that I don't have to use their DRM, and that if I wanted to, I could set up my own licensing server with my own way of controlling it. The problem is that that would be expensive, and I would have to do a lot of work to even figure out how to do it correctly - work that would be better spent improving MobileSheets. I could take MobileSheets off Amazon, but this would only serve to punish users who already purchased on Amazon, as they would never get any future updates. There are also some devices like the Kindle Fire devices that (to my knowledge) require that you get apps off the Amazon App store. If anyone has any expertise in this area (namely setting up a licensing server and everything entailed) please let me know, otherwise I'm not sure what the right answer is.
Mike
Mike