Even if that's true, that means LinkedIn is presenting a different site to the reader than they are to the search engine spiders, which breaks Google's guidelines and should be heavily penalized accordingly (as it would be for any mortals).

Google can spider every page freely, going from link to link without having to sign up. A regular user can't. Where's the penalty from Google for that? Why is so much LinkedIn content indexed when the user can't have the same experience as Google does? It's very blatant hypocrisy.