> I mean: how do they (the developer) make their earning?

That's an easy one ;)

In the beginning it's about different services and service levels. Single user with tiny online storage vs. Collaborative with unlimited storage and integrated PDM. Can you guess which one will be the paid one ? ;) But that's just an intermediate thing.

Ultimately, the business model is to get bought by a big player. When 3DS, Siemens, Autodesk or Google decide they need the technology. That's when money is made. VC firms bridge the cash needs and spin their rolodexes.