There's chips out there capable of tuning every digital TV standard: ATSC, ISDB-T and DVB. 

In fact, Samsung announced a mobile phone chipset supporting the three above plus the Chinese and Korean standards.

All of this is more or less irrelevant from the consumers' point of view. It's trivial to make set-top boxes / TV sets capable of decoding all three standards, and any of them has the potential to look good or terrible, depending on how much compression the providers use (theoretically ISDB can look better than ATSC, and DVB can look better than ISDB, but in practical terms they'll all look the same - pretty crappy except for the 4 or 5 main channels in each country; all the rest will be compressed into oblivion).

No mobile 1080i in Japan.

Sure, you can get it on your phone, but that's just the 320x240 1-seg part of the signal. 

The Japanese standard is really a bit of a pain to deal with since the actual high resolution broadcast is encrypted. In the US at least, there are quite a few options for PC HDTV tuner cards, whereas in Japan if you want a TV tuner for your PC, its either low res analog or the low res 1-seg signal.

I'd advise them to take the standard which will make the most and therefore cheapest and most advanced TV sets in the short term.

It's a no brainer.

Hint: unlikely to be DVB