Keep in mind the other notable differences between here and the US such as free health care, a larger number of paid holidays etc.
Also bonuses. Bonuses in London can be 100% of salary or more.
National health insurance is not really free in the UK... but UK contractors pay less tax than US ones generally. German freelancers get paid more, but pay more tax (and get more holidays).
Developers outside of London can earn less, but many prefer it.
I need to earn £50k to cover just childcare costs and the mortgage (looking forward to both of those going down soon). I could sell up and buy a similar property 5 miles away and those costs would both halve. I could sell up and buy a similar property 10 miles away and have no mortgage at all. Neither of those would make us happier as a family (no matter how much I'd love to have no mortgage); we want to live where we're living now, so I just get on with it.