Some people, when starting a fitness/nutrition plan, will find it very strict and hard to stick to. The common idea of a cheat meal is to give you that 'escape' from your strict diet, but you don't have to have one. Some people will be fine with the healthy diet and won't have any urge to have their favorite burger and chips. Sometimes it's not only your cravings that require a cheat meal, but your mind. With a tough training program and healthy eating plan, you could do with a 'reset' - a night off of your nutrition, a time to relax, eat whatever you want, and then get back on it the next day.
I have seen some fitness professionals who actually LOSE weight after having a cheat meal, and that's because their body just needed a break, and reset its systems. But many people think that a cheat meal is a must have thing, and there are some people who simply do not need a cheat meal. If you're 20 stone in weight and starting a healthy eating and fitness plan, then you do not need a cheat meal, as that could easily cause cravings, and you could very easily turn that one cheat meal into a more regular occurrence.
The concept of one cheat meal per week is a bit misleading, and people tend to think that they have to do it. It should be something that you do when you really feel like you need it. It's similar with training. You could be training hard for a few months, week in, week out, and then feel like you need a break - a few days off, which will be very beneficial. It doesn't have to be once a week, it could be once every 3 weeks - have a cheat meal when you think you could do with a 'reset'.
There's my view on the cheat meal idea. I do think people do it for the sake of it, even when they don't need it.
Lee Gregory Fitness