I've said this repeatedly: Facebook is a high-risk proposition, particularly as an investment (disclaimer: I work for Google). "Intent" as other commenters have noted is a big part of the story but it's not the only story. Search can broadly be broken up into at least two categories: 1. Navigational eg typing "b and h" into the browser; and 2. Informational eg "cheap flights to jamaica". I don't know what the make up…
Some people are just in a kind of Facebook daze.
"Hey, they had income for 3 years in a row. One billion last year. This is a sure winner."
They refuse to look at what Facebook actually does.
People will probably read your post and think you're biased because you work for Google. But there's a huge difference in what Google Plus can accomplish. You guys have the search engine data (intent) to combine with the social data.
So why doesn't Microsoft let Facebook combine with Bing? Then they would have a search engine. Or are they planning to do that already?