I'm going to not talk about the West Coast Mainline, as I'm party to information that I can't share.
However, a similar thing happens on the East Coast Mainline, where certain of the Hull Trains services call at Stevenage to pick-up at xxUxx hours or to set down at yySyy hours dependant on which peak we're talking about.
The reason they don't advertise this fact, so to normal passengers standing at Stevenage in the morning waiting for a train into London is that is that Stevenage is a FCC and a GNER station and the London-bound money from Stevenage is theirs.
However, obviously on a service like Hull Trains, money from Hull to Stevenage in a morning is perfectly fine as Hull Trains'.
Mind you Hull Trains is an open access operator.
As is Heathrow Connect, who last time I was at Paddington, which was a while ago admittedly, advertised the destination of their trains as Ealing Broadway, and then at the bottom of the departure board added "also calls at Heathrow Central"; thought at Hayes & Harlington and Ealing Broadway is of course shows its destination as Heathrow Central properly. Why do they do this? Well they want Paddington passengers to take the Heathrow Express!
Lets face it, if you're a regular customer at a station, and you know that a Virgin service from Manchester Picc to Euston late at night stops off a Watford Junction to set down only; and it does it every night, then you're bound to cotton on and jump on, you just have to know, as it won't be on the departure board at Watford as a service to Euston.
All of this topic is to do with Track Access Agreements between train operators, and flow of the passenger fares.