Google has lots of good reasons to build Chrome. Certainly embedding Gears in the browser is a good reason, that ought to also make former Netscape Constellation engineers smile. Dissing Flash is a always a good reason.
But what's the best reason?
Well, Google is still primarily a search and discovery company. So maybe the best reason to build Chrome is to deeply embed Google search throughout the browser.
I'm 70% through the Chrome comic, and I'm excited. This is a big event, and it's a big event that will benefit the entire user community.
All open source, and they mean open. Any competitor can take anything, thank you not required.
PS. See Andy, Google's not done yet ...
Update 9/5/08: Nice story on how Chrome was created.