After having lived in London for a few years, I noticed this everywhere too. I am no expert but I have a theory that it's a combination of:
Genetics - you'll notice this when you watch people walk and have odd knee/ankle flex.
Discipline - not learning how to walk properly. This sounds silly, but when you drag your feet and wear improper shoes injury is more likely.
Healthcare - I have noticed that people are more likely to go to the doctor compared to the States
Among older folks it is perhaps also related to nutrition - unlike the US, we had rationing through the war and well into the 50s so many people will have grown up with a barely adequate diet.
