Agreed; I got half way through setting up Google's 2 factor but then was told I had to use it for every login, instead of say when I was logging in from a different IP or doing some big change.
I am really, really happy to have 2factor auth for my gmail account. In retrospect, I think it's crazy I hadn't set it up before.
Although, I still think it's worth the added effort.
The downside, like I pointed out in another comment [1], is that even with (hypothetical) read-only access to your email account, a malicious party could arguably steal your accounts elsewhere on the net — that being the main reason why you'd want to have 2-factor authentication whenever possible.
But the trading the 2-factor auth for Google's disposable, device-specific passwords is not at all unreasonable.