Also Switzerland or Sweden have a lot of Apple users. All those countries have one thing in common: everything is very expensive there. So people have a lot of money and they can easily afford Apple products.
In Argentina for example an iPhone is around 2500 USD (100% import tax), an average citizen needs to save for a year to afford an iPhone.
A year?
A couple of years maybe, and you won't be getting the latest gen one.
An average Argentinian office worker should be able to put 2500$ per year aside. If he doesn't need a new washing machine or new furniture, he could get an iPhone. But he would need to spend all his savings just for one thing.
iOS is different from Mac right? There are a lot more phones than Macs in China I believe.
Japan has a higher share of iOS than the US or UK. Also China is ~20% iOS. Sounds small until you realize that percentage equates to more iOS devices than the US.