In response to a recent interaction problem with iCloud, Google has purposefully broken their CalDAV sync with iCal. From the Google Calendar Known Issues page:
Events deleted in iCal on Mac OS are not deleted in Google Calendar until further notice
In response to the above issue, we have stopped deleting events if the delete request comes from iCal. Until further notice, deleting any event in iCal on Mac OS will not remove this event from Google Calendar, but all other requests like creating events or changing existing events will be synced properly.
Spanning Sync, which uses a different sync technology than the CalDAV protocol used by iCal's built-in support for Google Calendar, is unaffected by this issue and remains the best way to sync iCal with Google Calendar. Boo-yah! :-)