Google are moving away from open standards. In the same way that they stopped using the iCal standard in favour of their own 'Google Calendar' API, they'd love to eventually force using some kind of 'Gmail API'.
the support CalDAV and CardDAV for Calendar and Contacts respectively, although i'm only using CalDAV for 2 public calendars, as i use iCloud for everything. And as far as i know CalDAV doesn't support invites at least from google.