My guess is that salary guides provided by recruitment agencies like Hays use numbers that are artificially inflated. They can write whatever they want, since they themselves come up with the report, and it's not audited by anyone else.

They need to give you jaw-dropping figures, so that you will question your current pay in your current position, and engage them for their services.

Frankly, I will only trust salary surveys done by the government, NGOs or other neutral parties without any ulterior motives. Unfortunately, very rarely do you come across a report like that.