From what you've told me, I assume you have the last checkbox ticked, inside Address Book:

So then from the iPhone's point of view, the contacts pulled from Google, to Address Book, will be no different to contacts originally created in Address Book (without the Google Sync). That is my interpretation and understanding.
Yes, physical USB connection will be required for contact changes to be reflected on the iPhone, if made via a MacBook Pro, without the use of MobileMe and solely Address Book with Google Synchronization enabled (checked, above).
-- If you want something over the air like MobileMe, then my suggestion is to purchase MobileMe since that is one of its selling points.
Otherwise, I have no answers or solutions for you sorry, since I physically plug my iPhone in as well for two reasons, anyway.
1. Charge.
2. Sync.
If I'm not doing one, I'm doing the other, the single connection serves dual purposes for me so I don't worry about any over-the-air business (I have no data plan) and it suits my needs/methods.
