This is somewhat tricky.
We can sell the Mac version via our website or the Mac App Store (we do both). Purchases made on one cannot be easily converted to the other. In fact, we have no knowledge of any information about Mac App Store purchases besides total sales numbers and basic stats like that.
Windows, the only really straight forward way is from our website.
Android, technically we could distribute from our website and/or the Google Play Store. Distribution from our site is not something I'm all that familiar with, but I don't think it's all that common these days. I'm sure someone will correct me if I'm wrong here.
iOS can only be purchased from the App Store.
As you can see, there's really very little in common between various distribution methods. We would _love_ to be able to sell a pack that includes everything. It's just not an easy thing to do nor is it possible on some platforms.
The only apps that actually have a real license for them is the website version of the Mac app, and the Windows app. The rest are all tied to the ID you used for purchasing (iOS, Android). The app also includes a software licenses section so you can store those credentials in the app if you choose. Making this a lot easier.
Hope that helps explain a little bit about why it might seem difficult, but it shouldn't be all that hard in the long run. It's like any other software really.
Kyle Swank
AgileBits