The reason that spam exists is the ability to impose costs on the receivers of the spam while the sender pays far less than the total of those costs. From what

The reason that spam exists is the ability to impose costs on the receivers of the spam while the sender pays far less than the total of those costs. From what I can see, tip4commit (and maybe bountysource, with which I'm not familiar) is exactly the opposite of spam: it introduces a way for those shouldering the costs of open source software to be repaid to some degree by the community.