how hard would it be to slap "http://" onto the email if it wasnt there? that way you get your email and you dont break the standard. not hard, not hard at all.
Most/all OpenID libraries already seem to handle identifiers without the http://
If the libraries don't already support the "@" syntax, they should.
If Google's way of doing things requires any proprietary changes, I'd say it's unacceptable, but if that's the only change necessary then it seems like a reasonable way of doing things.