I can't speak for a particular gig, and if the accountant rampant wasn't organising it, it could be dodgy. But there are a lot of misconceptions voiced here about the list.
When organised fairly, people are not allowed to f*** off for the whole day and then return to claim a spot in the front of the queue. There's not a hard and fast rule about the exact amount of time spent in the queue, but the majority of the time should be spent in the queue. Short breaks for toileting (PLEASE don't be a smelly hippy and ruin the gig for those around you, including Morrissey) and eating allowed/encouraged. If you're absent for too long, general opprobrium will follow and a stern but kindly man will have a good talking to you about that and may even boot you off your initial spot if it is particularly aggregious.
It may seem cliquey to you, but that is probably because you were not there early enough -- newcomers to the queue are informed without prejudice about the list as they turn up, but only up to a certain point. Depending on the length of the stage, the list may stop at a certain number because there's no point in keeping track of an unwieldy number with no assurances of getting a position at the barrier.
Also, people on the list are present in the queue, but they may like to speak with a friend who is at the end of or further down the queue or just returned from putting away chairs/going to the toilet. When it is time to sort out the positions right before doors, it looks to you like these people came out of nowhere and took a spot ahead of you unfairly, but that is likely not the case.
Yes but that didn't happen at the gig I went to. People didn't show up for a few hours while I was queuing and then all of a sudden they appeared and expected to be in front of me. Strangely, they all seemed to know each other. If there's going to be a list then everybody who arrives at any given time should be informed. We walked off again not even knowing about the list around mid-day and as I know that place pretty well it's extremely unlikely that there were more than 3-5 people there at the time. they could have at least mentioned it as I thought it was clear what we were there for, although admittedly neither of us had a quiff.