this seems like a conniving way to drive more traffic to google.com so people like my parents will then type in the urls they already know into google's search box
I can think of two reasons:
For beginners having 'address is the square box on the left and search is the rounded box on the right' is the sort of simplification Apple likes to bake into their products.
The other is 'The bit of the internet you are looking at is in the square box, and the 3rd party app for search called Google is over there in that rounded box (where it should stay)'.
Both make sense to me if I put on my Apple mindreader hat... although I may be being a bit too cynical with my second reason.
Type a search string into a 'universal' field and hit enter = perform a search.
Type a URL into a 'universal' field and hit enter = go to that URL.
Use some refined heuristics to determine the intention (ala the AwesomeBar in Firefox) and you've got the best of both worlds.
I don't use Firefox/Chrome daily, so I may be missing something, but I don't see why a dual address/search field needs to communicate with Google to be combined.
Safari could also use the Chrome-style status bar overlay.
Why have two search boxes when a regular expression can easily and accurately decipher what you are searching for?
Why does having two types of bar add anything but noise to lives of even the most advanced users (of which I include myself)?
The URL bar is a relic akin to the human appendix or tail-bone.
Begone.