Is this based on average income or median? I'm guessing it's average as wealth inequality is going to skew things higher.

In Japan, the median salary is ~3.5 million JPY pretax (~48% of people make between 3 and 4 million gross) and big cities are helping that a lot. It would be roughly 2.55m after tax (a bit north of $16k USD as of today). That's not buying a lot of big macs.