Thanks,
I understand what your saying that a .com and a .us domain are equal and other factors will determine rankings...
But argument against your statement is how comes a EMD that is .co.uk out ranks a .org.uk 10 fold?
This info sheet from Google imply's geo-targeting in webmaster tools will improve your rankings for the chosen location but also says if no location is specified then the domain extension will be the indicator.
https://support.google.com/webmasters/bin/answer.py?hl=en&answer=62399
Cheers