Would anyone please enlighten me?

How do cloud base online apps work actually?
I mean: how do they (the developer) make their earning?

They will have to spend time and energy to maintain the app, right?

Btw, it looks like a great program. Honestly, it's very similar to how i imagine the next MoI v4 will be
(in terms of simple UI and polygon modeling support... but hey, no push here... ;) ).