One difference that is very important to me, Hipmunk (and most other companies) are actively working very hard to improve the user experience and overall usefulness of theirs sites. Craigslist is doing the opposite. They are expending energy to make things worse for their users and customers, by shutting down third party sites. If you were to ask the people listing the properties, they would want their properties to be accessible via PadMapper. One motivation for CL to shut down third party sites is to minimize the efficiency of a listing being fulfilled and removed. If an apartment is found immediately and rented on PM, that is less revenue for CL.

CL are entirely within their legal rights, but they are in a position of great power, they are doing absolutely nothing to improve life for either side of the transactions they broker, and they are making the world a worse place.