have you found that google.com does less geo-targeting than country-specific TLDs, like google.ca or google.co.uk? What reasons do you think, if any, that this would or wouldn't occur?
it's because it's global for all users ,A global visitor would be never interested in other countries search results..
Thats how it supposed to be. A .co.uk is uk based by default. For .coms it probably need some SEO works to imply the local vibe.
The .com is known as a global TLD and most of the people uses that where Google's ccTLD and auto detection isn't available.