Recently I have started noticing more and more foreign results for searches despite by region set to the US. I searched for 'Wilson Pro Overgrip 30 pack' with the region set to US and out of the first 10 results, 3 were European websites and one being the fourth result in the list. I have attached a screenshot of the results (will require some zooming in since its a scrolling capture).
If the region is set to the US, then results from that country should be prioritized over .co.uk domains and other European sites.