I suppose for some passengers, having being bitten once by looking only at departure monitors and destination blinds, will tend to ask staff (or anyone) where a particular train is going to.
Im a fairly confident rail traveller, but have been directed to the wrong trains twice in the past by platform announcements and screens. Once was at Preston, bound for Blackburn and myself and a good 30 other passengers boarded the Manchester Victoria train because both the screens and the platform announcements said the train was for Colne. Having been bitten by that one, a few months later was at Birmingham New Street, bound for Northampton... and having to quickly get off and move to another platform, because that unit was now going to Shrewsbury. It even said London Euston on the display on the unit when I got on!
So I am a little less critical when I hear folks asking seemingly dumb questions; they've probably been caught out before by the railway (and lets face it, for most people it is still one railway, one company, one operation). Of course, when the opportunity arises, I still take the time to misdirect the occasional person who, if only they took the time and their head out of their bottoms, could figure it out for themselves.