Tom Anderson wrote:

Okay, so maybe it's not 6 tph. It'd still be pretty decent for an NR line.

Actually, the frequency of trains *to a Central London terminus* at
many stations in my part of the world is at least as good as that. Off
peak, for example, Gipsy Hill has 4 tph to Victoria and 6tph to London
Bridge (4 via Tulse Hill and 4 via Forest Hill), which makes 10tph "to
London". The problem is that, unlike Tube lines with end to end
running, they don't serve the same intermediate stations. This is fine
if you just want to get into Zone 1 quickly, but if you need to get to
Clapham Junction the frequency suddenly drops to 4tph.

The service at North Dulwich and East Dulwich is far more 'tube-like',
at least in the northbound direction - all trains go to London Bridge,
calling at the same stations, and at regular 10 minute intervals. Which
makes it feel much more 'turn up and go', but is a real nuisance if you
want to go anywhere other than London Bridge!

This would be a major argument in favour of simplification (as
discussed somewhere else in this thread) - but I think most people who
actually use the services regularly get used to having to look at a
timetable, and appreciate the one-seat ride to either London Bridge or
Victoria/Blackfriars or Victoria/Cannon St or LB/Waterloo East/Charing
Cross.