You would be surprised at what goes on. My job role means I see the figures across the many companies I have worked for. If someone is off sick for a long time, it's usually easier to give them a year's salary to wave a 'mutual' good bye. Also stops industrial tribunal.
I've seen some very high payments, where someone is retiring of their own choice, is in a very high position, then 'negotiates' a very substantial well into six figure 'pay off' with senior staff - makes you sick when you see it as you realise some people are in it for themselves, what ever they may have 'told' you to your face prior to that.