Your counter-example (ms windows+expolorer) is not-quite on point, though. Consider: windows
had a legitimate monopoly, and then they "abused" it. But, because you are presuming the existence of a monopoly for CL this does not work. CL is an online classified ads business. The barriers to entry are de-minimus (unlike, OS software + hw compatibility, ect). So the
premise of monopoly can be attacked fairly and directly.
CL arguably is not abusing a monoploy because they don't even have one. They just have a cheap service, and nobody wants to pay to do it different. The consideration you raise -- are they anti consumer -- is an interesting one to think through. It does seem they over-reached (re: the exclusivity of data). But without any contractual exclusivity or confidentiality its not clear that CL can "monopolize" publicly published data, given that the most valuable bits are (at least for rentals) nothing but street adresses, apartment #s, and possibly Telco #s. These data are not legal-sense "intellectual property" under most concepts (patent, copyright, or trade secret).
It would be an interesting argument to see the threshold case: when/where do 3 facts become a creative work? Its not a trivial argument, though, because at some stage N words becomes a lyric a poem or an idea. You cant copyright a word, though. Its highly unlikely you can copyright an adress. They might try to argue its like a "recipe" or some such (list of common ingredients?). Who knows. But somewhere in there, I'm guessing we'll find out.