Putting an "word" in "quotes" is the inline way of exactly matching an individual word. It's conceptually similar to putting a phrase in "quotation marks," so personally I think it makes sense that we have one operator for literal searches.

> A + could apply to a single word or to a single phrase

I don't think a + could apply to a phrase. That was one problem with the + operator; it was not clear to users how it actually worked. In fact, though there were many searches whose results were helped by their use of + (many of whom made by users who are commenting here on HN), there were many searches whose results were largely made worse by their use of +, whether it was inadvertent or overzealously applied.

That was the AltaVista innovation, and one I'm sure Google is happy to weed out of everybody's minds regardless of the fact that it works and works well.

When Google first appeared on the scene, I remember being disappointed in its lack of tweaks, compared to AltaVista. However, the quality of Google's results quickly won me over.