This is true in many cities. I've personally seen subway frequencies in London, Seoul, and New York that are far less frequent than our most infrequent line, at the most infrequent time of day (barring service delays).
Our most infrequent subway is Sheppard, and off-peak it's still about 11 trains an hour (once every 5.5. minutes). The other 2 lines are always better than 12 trains an hour.
Look at the L train in New York (which doesn't even have any branches). In central Manhattan - at midnight with relatively busy platforms, I've waited 20 minutes for one (looking at the schedule, they've now improved it to a 10-minute frequency at that time - 6 trains per hour - 20 minute service starts later now). If you look at the timetable -
http://www.mta.info/nyct/service/pdf/tlcur.pdf - they have 6-8 minute gaps mid-day and start the 10-minute service at 10:30 pm!
Check a busy London tube line, like the Picadilly line. Departures from Terminal 5 are only once every 9 minutes at 10 pm. It's only once every 10 minutes at 8 pm ... and that's a weekday!
The bus frequencies on many of our routes are amazing - even off-peak. I don't think a lot of people really appreciate what we do have, and only focus on what we don't have.