I seem to remember when they were telling us that HDTV and digital television would bring an end to having two major TV systems that were incompatible without conversion. However, with HDTV, we now have four different systems, all directly incompatible. Japan has developed ISDB-T and spread it to the Phillipines and all South American countires except Colombia. China has its own system, called DMB-T. The other countries of Eurasia, Africa, Oceania and a few others have DVB-T and North America uses ATSC. How and why did this happen?

South Korea also uses ATSC. And Europe uses DVB-T.

The full map of the scattered standards is on Wikipedia: https://secure.wikimedia.org/wikipedia/commons/wiki/File:Digital_broadcast_standards.svg

My only issue with Digital Terrestrial broadcast is that it is impossible to pick up when you're moving. And it's all about line-of-sight too.