While Google have an interest in talking about the message that Gmail is secure, from a security perspective it's kind of naive to say "Gmail is secure".
All web mail (or any other system) is just a step away from the next exploit. The difference in my mind between web mail and regular mail is there another dangerous attack vector (XSS) which is only fixable by a single vendor.
The standard mail servers companies use are often vetted patched from many sources and can be hidden behind some pretty well tested encryption protocols.
Trusting mission critical things like domain name registrations to web mail seems like an unacceptably big risk to me. While XSS wasn't the issue this time, it clearly has been in the past.
