China has the critical mass of population, money, foreign investment, finance, and industries.
The same reason why we can't have a nice downtown (not enough population living there) is probably one of the critical reasons why we can't have nice buildings either. It's difficult to justify the cost when there's only one or two big O&G players every decade that might want a new building. With Imperial moving to a big box in the burbs, it might even go the opposite direction.
If you've been to China, you'll just notice the incredible amount of people and density that makes it worthwhile to build nice things because there will always be people and money to make it worthwhile to have it and in that culture. Even a small little village outside Shen Zhen is bustling at night with more shops and restaurants late at night than any location in Calgary. (South African guy walking around a village explaining why there are no Laundromats:
http://www.youtube.com/watch?v=MqUFkjjy-I8&t=7m35s)
Displays of opulence, wealth, and grandeur are also important in that culture.
Finally, the weather sucks here. As others have said, the necessities of dealing with the temperature fluxes makes buildings conservative and when it's cold, everybody just stays home in the suburbs so there's no critical mass to create any sort of cool-looking dense architecture.