Willesden Junction and How Not to Sell Train Tickets

I feel like having another moan about train operations at Willesden Junction. Before Christmas, I went down there to buy a ticket on the mistaken assumption that it would be easier to talk to a person than buy the ticket over the Internet. There were three ticket clerks there. One was selling the tickets, and the other two appeared to be employed to look at her selling tickets. When I enquired about my journey, I was told that the staff at Willesden Junction do not have access to information about all the possible journeys and I might be better off just buying a ticket on the day. How is it possible that the train operators don’t give their staff access to such basic information?