If users want equivalencies then they shouldn't use quotes, which are for exact match. Let's not play semantics here. Search syntax is clear - put things in quotes, get 'exact match' in return. Equivalent words are not exact match. Get smart with me, decrease usability for me. This is what is happening.

We can argue whether there is place for more operators, or whether it's better on average for an average user to still be "outsmarted" by the engine, but it's clear what's going on - these aren't exact match results and the results often have zero relevance with what user is looking for precisely because the user knows the specific word WILL appear on the page they need and a page without that word WON'T be what they need. I don't know how much clearer we can be :) It used to work (or seemed to). Now it doesn't. It frustrates some people. That's it.