"We're a domain registrar and we definitely recommend trying to purchase your domain name in as many TLDs as possible..."
Please do not take any offense, but as a domain registrar it would naturally be your position to advise others to buy as many domains as possible. You likely would also advise customers to register the domains for as long as possible too. Both courses of action generate revenue for your business. That does not make it wrong advise, but rather you are not an unbiased source on this topic.
"Google will rank .CO.UK better for searches coming from the UK, so that could be handy if you decide to break into certain markets outside of the US."
The TLD or ccTLD is one of over 200 factors which involve a page's placement in search results. Site owners can also demonstrate relevancy to a given country by hosting in that country, setting their language code for the target country, earning links from the country, etc.
It would be helpful is if you can present any solid evidence to support your recommendations. Information from Google, Matt Cutts or highly reputable sources of information would be great.