In other words - Google acts as an OpenID Provider - you may recall that even your Blogger urls are OpenID enabled.
Google's support to OpenID is through the OpenID 2.0 Directed Identity protocol.
Directed Identity is a term introduced with the seven laws of Identity and it says,
"A universal identity system must support both ‘Omni-directional’ identifiers for use by public entities and ‘unidirectional’ identifiers for use by private entities, thus facilitating discovery while preventing un-necessary release of correlation handles."
Under the OpenID terminology 'Omni-directional’ identifier is equivalent to the OP-Local identifier.
With Google, you can login to any OpenID RP by entering Google OP-Local Identifier, that is https://www.google.com/accounts/o8/id.