I'm not from UK, but I guess that even if you visit the slums of London it will look similar to a middle class neighbourhood from a third world country. The fact we get surprised by all the wealth of a city like London is due to being used to the reality of our native countries where poverty, misery, dirt and thieves are lurking everywhere, including central, touristic areas. At same we don't have much notion of the reality of first world countries, getting really surprised once we see it for real, people from these countries also don't have notion of the third world countries' reality, and may get shocked if they see it for real someday.

Probably OP didn't see only tycoons on his journey through London, but the fact even the average citizens walk dressed in quality clothes and display good manners in public already gave the impression they were wealthier than they really are on the eyes of someone who isn't used to this reality.