I assume-
Brand loyalty is not a big thing for customers going into multinetwork stores. Customers staying with the network will get a good deal from the network itself.
Customers going into CPW or phones4u would be open to any suggestion except, probably, the one they're with. I bet they didn't even notice if one was missing.
The biggest hooks are the phone and the cashback.
So the absences would only be marked when the phone was an exclusive to vodafone.
In my experience, it's always better to do your own research them go direct to a network store. you'll say more, but it helps when things inevitably go wrong.