It's funny because at 40 I still compare prices to 20 years ago, which is stupid as income has also gone up.
But YES it's a lot of money. .But it may all just be about perspective. I grew up "poor", as in parent on benefits and free school meals etc. I'm from London and did a sting there in 2007 but came back up north.
Just going on then, as I've not tried to live in London since, rent for a room in a shared house was £500/month. I moved back up North three years later and rented a studio apartment for myself at £320/month.
That gives you an idea of the disparity.
If you're trying to live a responsible adult family life in London (home insurance, travel, educational activities, days out) then I can see how 100K would not go far in London.
Take the same family life here up North and you're talking luxurious living. I can say that as we live pretty well here and our family income is 40-50K at most. We have one child and we have lots of insurance things going on (hubby does those) and at the end of every month we do find things tight until payday, but the house we have and the things we do are all managed comfortably on our collective income. I don't even work full-time.
So it's relative, but by most standards, YES it's a lot. Global standards, and the fact most people living in London are living on a lot less.