Earlier quoted context omitted.
>the idea is that the product becomes more valuable over time as a result of more features being added I have a hard time believing that's the main motivation
Was the same licensing method for Minecraft in beta
Interestingly, I've seen some devs turn the concept on its head and charge more up front, kind of to say "only buy in now if you are really doing this to support development, and in return you'll get an early release build - but you aren't buying the game early."