Not surprising; I'm guilty of this, too. It's mostly because I can no longer figure out what the long white boxes at the top of my web browser do.
For example, with FF3b5, if I type "google" in the URL box, it shows me google.com search results for the string "google". But if I type in "amazon", it goes straight to <http://www.amazon.com>. What's the pattern? I have no idea.
(Reads the docs...) Apparently the URL bar first goes to a "keyword search service" (default, google), which will automatically redirect, or show search results. If you disable this, it does "domain guessing" (adding ".com", etc.).
Geez, I'm a web developer, and I had to read the docs to find out what the URL box does these days. I feel old.
I've definitely seen people get to google by searching for "google" on yahoo as well.