Earlier quoted context omitted.
It's not "their" data. It's their user's data. As a user and a homeowner I post my rental listing to Craigslist because that's where the most prospective renters are. In the past, do you think anybody ever looked at the classifieds page in a newspaper and thought "this data is owned by the Times"? In the PadMapper case, who are the losers? Renters benefit from a radically different UI and de-cluttering of daily repos…
It might be your data, but that doesn't somehow make it Craigslist responsibility to share it with other applications. If you want your data listed in as many places as possible, register with each and every system, and enter it. In the past, do you think when you submitted a classified to 1 newspaper, they called up all the other local and regional papers to submit your information too?
Nobody is expecting craigslist to push data to 3rd parties. They expose programmatic ways to access listings, and PadMapper used them.