I'm not sure I buy this argument.
What if Padmapper folks were to create a site, lets call it PadBay and start scraping eBay lists and then provide a nicer UI, auction format and so and so forth, technically the same argument would apply, but eBay would rightly go after PadBay and would be correct.
The data that a user has posted to CL is indeed CL's data since CL is storing it. CL is not claiming copyright on the item, rather the post to CL.
The user is indeed allowed to repost it elsewhere and that would be that site's data.
This happened about 10 years ago when eBay sued Bidder's Edge over its scraping of eBay's listings to gather statistics [1]. eBay sued, and although the case was never fully developed, the preliminary injunction issued against Bidder's Edge killed off an entire cottage industry of auction tools and analytics services, including the company I worked for at the time. I believe it also helped solidify eBay's dominance in the online auction market as the disappearance of these services made it much more difficult for buyers and sellers use multiple auction providers (anyone remember Yahoo! Auctions?) in an easy way.
The data that a user has posted to CL is indeed CL's data since CL is storing it. CL is not claiming copyright on the item, rather the post to CL. The user is indeed allowed to repost it elsewhere and that would be that site's data.