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.
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.