OK; my point was, if you know the name of the function you're looking for, you get PHP's search.
If you misspell a function, you get PHP's search.
If you search the "entire website for the string $foo", you get the thing you're talking about.
And, I don't know that I fault them for using Yahoo!'s search. Why reinvent the wheel? Plus, Yahoo! generally tends to be FOSS friendly ... although I don't like some things about their organization....