In fact, dpcan has managed to convince me that he's right. When I search for the title of a book, and I get to see a preview of a few pages, it is a form of advertising. It's not "wrong" or "mischievous" or "evil" or any other negative, it's just how advertising works.
The reason you are all upset is because that's not how Search Engines, in particular, worked. With book previews on Amazon, we're used to it. What EE did was try a new tactic, built for the web, to advertise their product. Of course we didn't like it - when has anyone ever liked paying for something?
Nowadays, what they do has been ruled to be wrong. The "rules of the game", as defined by Google (the authority here, apparently), say that they aren't allowed to do that. They find "tricky" ways of doing it, which sucks. But remember, these rules are being written live - you can't hold EE at fault for trying to "hack" a system, and you definitely can't fault them for not living up to rules that never existed.
There seems to be two different complaints about EE.
1. They show data to Google but hide it from visitors unless they pay. Personally I see nothing wrong with this as explained by edanm. They are a business and this is their business model. They use a search engine as a form of free advertisement. If the search engines didn't have a problem with this then I don't understand why potential visitors should. If you don't like having to pay for the content then go elsewhere. Having results in the search engine that have data behind a paywall is the problem of the search engine, not the site that has the paywall. The data is still relevant even though you can't see it immediately on clicking the link.
2. They show one set of data to search engines but show a different set to visitors. To me, this is a no-no as long as they are actually doing this in the described manner. If by showing different data is because of the paywall and they do match up after you pay, then I see no problem. But in the end if they do not match then there's a problem and I would hope that the search engines would discourage this type of thing.
I think people need to be more clear on what exactly they are complaining about.
Plus, as edanm states, you shouldn't down vote someone simply because the statement is unpopular yet relevant to the topic.