Literally the same thing, here.
I'm just assuming it works this way, as passing the password along would defeat the security of the system and make you more vulnerable.
I literally don't see a major difference here, except that now we're using email instead of whatever bullshit identifier you could have used with other OAuth providers (e.g., your Livejournal username, your Facebook account, etc., etc.)
If I'm wrong, I would love to be enlightened.
The major difference is it's totally irrelevant to the site (relying party) what provider you're using. The site doesn't need a login page with a facebook button, a twitter button, a livejournal button, etc., it just needs a "sign in" button.
Even email isn't safe, unless all the OAuth providers validate the email. Does Twitter allow me to change my email address to "president@whitehouse.com", and then return that to OAuth consumers as my email? I don't know.
There's too many things ways to shoot yourself (or someone else) in the foot.