Since the digital switchover you have to retune your tv in the US by the way.
Yes - but there is the bizarre ATSC system that allows digital stations to use their old analogue frequency as their new LCN-or-equivalent isn't there? Plus the .1, .2 sub-channel system that the US has that is almost unseen elsewhere.
This whole "old analog channel as digital LCN" also happens in countries with ISDB-based systems, such as Japan (where the system was originally developed) and here in Brazil (where enhancements to the system were added). In fact, here in Brazil, subchannels do exist, though only public-service channels are allowed to use them.
For example, many cities (such as here in São Paulo) have multiplexes for the legislative and judicial powers.
Here in São Paulo, the legislative mux (digital-only, on RF channel and LCN 61) carries:
61.1 - TV Câmara, the channel for the federal Chamber of Deputies (the lower house of our Congress).
61.2 - TV Senado, covering the Senate.
61.3 - TV ALESP, covering the Legislative Assembly of the state of São Paulo (each state, and the Federal District, has their own single-chamber parliament).
61.4 - TV Câmara São Paulo, covering the Municipal Chamber of the city of São Paulo.