Garage mechanics are paid far more for a job monkeys can do. £120 per hour to change the oil in our local dealership, apparently.
Plumbers charge £60.
Statistics are very dangerous tools if they're taken out of context. In the examples you cited, in the first case you're not paying £120 to the mechanic as hourly wage, you're also paying for the whole workshop including tools and machines that the mechanic needs to perform the work you need. In the case of the plumber, again how many hours of the plumber's time was required to perform the work? Since he probably doesn't share your living quarters, he actually had to get to and from your house and that might take some time. Then there's tools and so forth and so on.
To get back on topic, professional pilots spend a significantly higher amount of hours at work than just the actual flight hours they log. Simply dividing average pay per average hours flown/month is just plain idiotic.