I understand the essence of your point and agree with it to some extent, but I think in this instance I wasn't clear. Google are transparent about their process and let me know they'd vote on it at their next meeting. I've clarified the language in my post.
The idea of an intermediary is an interesting one, certainly for smaller companies. However, for the company to be able to work out the value of the bug, they'd need to know enough details to 'score' the bug such they could maybe find it. Either way, you'd end up needing some trust.
However, the idea of a service to manage all that for small companies is a good idea. It reminds me of the Common Vulnerability Scoring System (http://www.first.org/cvss) for scoring such exploits.
But I also don't see how that would play out. If their offer is too low what would you do then? You can't sell it to someone else as this is most likely illegal and just keeping it for yourself is also not a great choice.
That aside, having another party getting advance knowledge about the bugs is risky: it just gives bad actors a juicy target to infiltrate to get a steady supply of 0-days.