[This is unchanged in Yosemite and I suspect is also true of El Capitan.]
This is what Mountain Lion shows as my Calendars as of August 2013 after standard setup against my Gmail account:
The accounts I see under "Google" are the set of Calendars my Gmail account has access too that are also checked in the web page that controls Google CalDAV access for iOS Calendar.app: https://calendar.google.com/calendar/syncselect
The Delegate list is what appears based on my selections in Calendar:Preferences:Accounts:Delegation, where options include ALL calendars known to Google, not just those selected in https://www.google.com/calendar/syncselect.
If I check all of the calendars in Calendar.app (Mac) I'll get duplicate entries. If I disable "delegation", which appears to be Google's undocumented recommendation I get a neat list, but any changes I make in Calendar.app do not appear in Google Calendar (sync is broken, or, if you prefer, it's "one-way" from Google to Calendar.app).
If I uncheck Calendars under the 'Google' tree in Mountain Lion Calendar.app "Calendar List" and just use the Delegates sync is more-or-less bidirectional (not broken). That's what I'm doing for now.
I once thought Google was responsible for this mess, but given Apple’s software bungling over the past 4-5 years I think it’s more likely their issue.