Interesting. I would have guessed that it would have been the other way around. Go far enough North, and DST is pointless because they're just isn't enough daylight no matter where you put it.
Also, your comparison on latitude is a bit off. London is at a higher latitude than Seattle, for example. It just doesn't get as cold, because you have the Gulf Stream warming it up.
Wintertime there definitely isn't enough daylight to go around here, but staying on summertime meant that northern England and Scotland wasn't having sunrise until nearing 10am. Dark mornings, it seems, had more effect on accidents than dark evenings.
I just picked southern parts of each nation, rather than checking. It may be that it is more relevant to Canada than US, excepting Alaska. :)
Work and living patterns have changed quite a bit in 50 years too.
China has only 1 timezone, which is based on a city on the east cost. In the west part of the country, the sun always comes up and goes down later than what we east coasters consider as normal. However, they got used to it anyway.
Time zones are artificial and don't make it too complicated. Pick a simple solution and let people adjust.
From what I've heard, in Xinjiang (the westernmost province of China), the locals completely ignore the Beijing timezone rules and work on a local timezone that's two hours off, although that's also in part a (relatively) benign form of civil resistance against the unwanted Chinese government.
Also, your comparison on latitude is a bit off. London is at a higher latitude than Seattle, for example. It just doesn't get as cold, because you have the Gulf Stream warming it up.