Perhaps it's as simple as CL has no way of determining who is on the other side of the pipe. In Craig's quoted statement about RSS feeds, it seems that they are concerned about commercial use of CL data. If Yahoo Pipes essentially masks the origin of the request, then it makes CL's job more difficult.
As for determining motive -- profit or otherwise -- I suspect it's more about keeping others' greedy mitts off their community than cold cash. CL has been about the community of people using it since it was just a mailing list, and publicly Craig and Craigslist have been pretty clear about what they value. So, they probably see pipes as a threat to that community.
As for determining motive -- profit or otherwise -- I suspect it's more about keeping others' greedy mitts off their community than cold cash. CL has been about the community of people using it since it was just a mailing list, and publicly Craig and Craigslist have been pretty clear about what they value. So, they probably see pipes as a threat to that community.