My wife's travelling from Wandsworth to Watford Junction tomorrow, so
I looked at the price of Travelcards for her. Can somebody tell me if
what I've come up with is really true?

* Price of an All-Zones Travelcard: £5.40.
* Price of a Travelcard from Watford Junction: £9.80.
* Therefore, price of a CDR from Boundary Zone 6 to Watford Junction:
£4.40.

But...

* Price of a CDR from Hatch End to Watford Junction: £2.60.
* Price of a CDR from Harrow and Wealdstone to Watford Junction:
£3.00.

I guess my question is: why would anybody buy a Watford Junction
Travelcard or a BZ6-WJ fare? Do I have this wrong somehow?