With google calendar, you don't get "true" syncing. It will not take previous events on the iPhone and "upload" them to google calendar. My wife had updated her March calendar on her iPhone. She then added google calendar. However, all the March events she had previously added to her iPhone were not sent to her google calendar.
Also, once google calendar is installed all calendar information that is entered is owned by google calendar and not the iPhone calendar. This means if you decide to remove google calendar from your iPhone, then any calendar information you had entered while you had the google calendar will be removed from your iPhone (note: it will be in your google account, it just isn't kept on your iPhone hard drive).
A true sync would have all the calendar information on the iPhone copied to the other calendar and all the information on the other calendar would be copied to the iPhone. I believe this is what actually occurs when you sync with Outlook.