Technically they don't break any of Google's rules. Google's First Click Free initiative is designed to allow paywalled content to be crawled and indexable, subject (among other things) to guidelines like:
- All users who click a Google search result to arrive at your site should be allowed to see the full text of the content they're trying to access.
- The page displayed to all users who visit from Google must be identical to the content that is shown to Googlebot.
Now, these are true for EE, but the page which is shown to both Googlebot and users who've clicked through from Google is very obviously geared around making you think you have to pay to see the answer which is at the bottom of the page.
Also, Google only requires that click-through users see the same content as Googlebot. It doesn't require that a casual user sees the same content. Experts Exchange is in effect a paywalled site and you should think of it in the same way you think of other paywalled sites.