Could this be that because our infrastructure and speeds for BB is so poor compared to other countries, we are not put off by the lower throughput and potential interference issues? If my broadband was the usual feeble 1-2mbit connection in the UK, knowing that my devices are not going to be missing out any bandwidth if I use a 802.11g (or even b) home networks compared to the ADSL connection's maximum would mean less work compared to wiring the whole house with cat5.
On the other hand, if I was plugged into a 1Gbit connection in Sweden, chugging my device along at 'g' speeds would be a complete waste of potential speed and money.
I have no idea why the south Koreans are big on WiFi though - more densely populated areas?