Nope. I have transited through LHR or LGW on my way home to Australia from the US on OWE fares. My regular jaunt to DFW is cheaper on a RTW ticket, so I retuen via Europe and Asia, but the only place I stop overnight is DFW. Done this lots of times. Costs less money and get more miles (though I don't max out the miles - I still have to survive the trip).