This information is freely available on their website (not to mention their widely distributed paper catalogs). Google has crawled much of Digi-Key's website and has this information on their servers. However, Digi-Key is specifically targeting Octopart (actually, I'm not sure if they're threatening Google, my uninformed guess is no though). The only thing we're doing differently than Google is distilling the information in a way that allows part buyers to compare prices readily. There are other part information websites also crawling Digi-Key, but Octopart is one of the only ones doing price comparison - again, I'm just guessing, but I doubt Digi-Key is threatening any of these other websites.

Also note that courts have generally held that pricing information is not protectable by copyright (prior to publication it might be a trade secret, but once you publish it, it essentially becomes a fact in the public domain). This has not stopped large retailers from using novel legal theories (or carefully timed DMCA takedown requests) to stop or chill 'Black Friday' websites, of course, but the law is actually reasonably clear in this area.