Scottish City Link must be an exception then. Just last Monday, the ETA of a coach I was expecting to catch at 1130 was important because (a) I had a connection to make with a train that, in the reduced timetable, was one of only three schduled that day (and the third would, in the event, be cancelled) and (b) it was pouring with rain and there was no shelter at the bus stop.
Seeing it had been on time at 0830 but had apparently not yet reached the next timing point five minutes further on, I phoned SCL who assured me the bus was running to time and two minutes later the online tracker data had been updated - albeit to "data not available", but that was better than "not moved for an hour".
And it did arrive, not more than five minutes late which, given it had been going for five hours already, was not bad.
Problem with "delayed" is that, at least on SWR, it then appears in the "1st" "2nd" "3rd" sequence at the time it should have arrived, ahead of any trains that are running. Thus, at somewhere like Wimbledon, you will see nonsense such as
1st train - xx03 Chessington - approaching
2nd train - xx06 Woking - delayed
3rd train - xx09 Shepperton - 2 minutes
In practice "Delayed" means it hasn't left Waterloo yet, and so there is no way it can arrive before a train that is only two minutes away. It also crowds out trains that are actually close at hand.