Yes this ratio was something we thought of a lot. There are two aspect here that we were thinking about:
Abuse. If the community part is large then its easier for spammers and cheaters with a little SP to abuse and get a big piece of the reward, especially when the creator of the bounty does not have much SP.
How much control do people want to have when they send the funds. We assumed that people would want to be able to decide more how the rewards are being distributed.
Later we will allow users to chose the distribution. We are working on getting the website up, and then more features will come after that. We appreciate the feedback!!!
You have a strong reason on the issue of Abuse. Assuming one makes a comment under a bounty-bound content, it's withing the realm of possibility for them to copy the link of the comment and distribute to their friends, soliciting for their votes. I understand better now. Thanks for the explanation...I'll try this out soon, for now my wallet is weak to give out such fund.