Hopefully this doesn't mean they won't be showing up in padmapper and other apps like that. It's a pretty useful service while apartment hunting, although it would be awesome if they could find a better data source than CitySearch.
That's almost certainly what this means. Proprietary datasets are VERY hot in real estate right now because otherwise, everyone is working with the same listings data.
Did you know that Redfin is a very popular website with real estate agents who compete against Redfin agents for customers? And this violates the redfin.com EULA (real estate data is for provided for prospective home buyers and potential customers), but is not enforced at all?