Certainly in some cases the .co.uk site would be more relevant to a UK searcher, but that is not always the case. Google’s Matt Cutts has posted a video in which he answers a question on this subject from a user. The question was:

Why are the UK SERPS still really poor with irrelevant non UK sites (US/Aus/NZ) ranking very high on Google.co.uk since early June?

Cutts says it is true that searchers in the UK will see more .com results, and that is simply a product of Google getting better at determining geographic relevancy.

As Google gets better, they’re more willing to show .com results if they’re relevant to the country. “If the best result for a British searcher is something that ends in .com, we still want to show that to that British searcher,” says Cutts.

According to Cutts, this is a change that Google will not likely reverse, although he does encourage users to let them know if they see such results that aren’t relevant, because they would want to improve this.

The bottom line is that Google is just learning more these days about what sites are associated with what countries, and they’re better at detecting it. The goal is to supply relevant results.

As a bonus, Cutts posted to his blog that he’s already received some criticism about his answer in the above video and responded: