Glassdoor requires you to post your own salary to view the salaries of others (unless that policy has changed recently). So if you're browsing a lot of glassdoor salaries, you've probably posted your own.
I interpret that differently - that most of the people that posted their salary lied. Myself, for example, I've never posted my salary because I've always worked for companies so small that the employer could easily identify me. So if I wanted to browse the salaries, I would just make up a salary (around the existing Glassdoor average) for a big company (Intel, Google, JPMorgan, ...)
