There is an entire industry around the collection of and aggregation of salary, benefits, and perk information. Every year your HR department pays a firm, fills out these surveys, and a few months later gets a report on salary ranges and perks for their industry.

If you think about it then it makes perfect sense, how else do businesses know they're offering competitive salaries, benefits, and perks?

Source: I consulted for a company that does these surveys and aggregates the results.