On Monday, 9 October 2017 10:43:05 UTC+1, Robin9 wrote:
Is there any logic or consistent pattern to the way Chiltern
Railways serves the London suburban stations on the route
to High Wycombe? Marylebone Station feeds a minimal
suburban network and a straightforward, all-station-stopping
train once an hour would get the job done. Chiltern seems not
to agree.

Their method is to run trains to destinations way outside London
and very occasionally to stop a train at one suburban station.
That might be acceptable to someone travelling to and from
Central London but is quite useless for someone wishing to go
from, say, South Ruislip to Wembley.

Chiltern Railways is a commercially savvy TOC so I assume there
is some logic to their system.

The simple answer is that being "commercially savvy" they know they will earn for more money from passengers travelling beyond Gtr London. Therefore all their effort is concentrated in serving those markets - especially given the investment in the Oxford and Brum services. I suspect Chiltern would not stop at the Ruislips or Sudburys if they could get away with it but the DfT mandate a limited service.

To run an effective and attractive suburban stopping service would require investment in more platform faces and passing loops to allow fast trains to overtake the slows. Not going to happen unless the DfT insist on it and that's not going to happen either. The presumption is almost certainly that people will use the tube and buses for the sort of journey you quoted.

--
Paul C
via Google.