The mechanism the OP referred to was picking up an existing product and providing a more or less uninterrupted user experience. It's a great benefit for a start-up to be able to hit the ground running with a user base and traction.

In the case of Wave, there was a major gap between the product being declared EOL from Google and until the various bits and pieces for running Wave as an independent vendor was in place - and in that gap all reasonable people ran away, so non-Google Wave offerings are starting from scratch.

As for money, no, certainly not impossible, but it's one more hurdle to hitting the ground running.