"Ho" No Go Where "Lo" Do?

Last night I accidentally hit the enter key after typing "to" -- on my way to this blog -- into my Firefox browser's address bar and was sent to a completely unexpected website. Turns out the same thing happens in IE. Try it. (Right now.)

I completely understand sites can buy these keywords (or word stems) -- here's where you go if you type in "ho," "lo," "us" or "pm" for example. Those all make a good degree of sense. But why "to" brings me to the site it did, or why "no" brings me here, are a mystery to me.