Thanks for your replies! I asked this question in light of a semi-political debate I had in which I tried to remain as moderate as possible. You had those who claimed that it was easier to live in a "social welfare" place like the UK, and those who claimed that the USA's more "free economy" was better.
After thinking about it, I think what clouds some perceptions is the high materialism of the US. If you're disciplined enough not to buy things like a McMansion, SUV, etc. that you really can't afford, it becomes easier financially in America. On the other hand those who base their standard of living on relative rather than absolute terms would probably feel less pressure to keep up with the Joneses in the UK. Another way that the American system rewards frugalists who save is that many of the expenses that the US is worse on are big-ticket items like health care (which is one reason those with major health issues may find it easier in the UK) and higher education.
After thinking about it, the logic in the previous paragraph also explains one of the reasons why many American families claim they can't make it on one income anymore. If they didn't feel the need to buy bigger houses/vehicles/whatever than what they need, the latest in everything, etc. many (but not all) such families would find they probably could manage with one breadwinner.