It's scummy on the economist's side from a SEO perspective which I absolutely hate in all media outlets that do this.

If the full article is allowed to be indexed by a search engine, the expectation is to be able to get the _same_ result as the search engine is seeing when you click through.

This is clearly a cheap way to rank higher in search results. If you don't want non-paying users to read, then the same excerpt should be shown to the search engine.