Google does search for "for" by itself (
http://www.google.com/search?q=for) but if it's included with other words then it will only search for it if you put a "+" in front of it like this:
http://www.google.com/search?q=live+%2Bfor+speed
Apart from that, it's a mystery to me too - I haven't kept up to date on detailed syntax lately so it could be a feature that I don't know about.