Although this sounds like a decent idea, the challenge with it is that you're assuming a couple of things:

1) The start-up acquiring the lead list has the ability to progress the deals to closure.

2) The start-up acquiring the lead list is able to appropriately break-down their revenue in an easily audit-able/non-modifiable manner to demonstrate which $ came from the acquired lead list(s).

This type of thing may be an option for these guys going forward (once they figure out the kinks), but I think they're doing the right thing right now by charging up-front.