Absolutely no surprise to me at all. And, I don't think it is correct to assume that this is only photographers who work for others.
I've done the math myself and concluded it would be very hard to make a go of it. Actually, I'd love to hear what some of the people on this site who do this full time make.
When I've done "back of the envelope" calculations it seems pretty tough. For example: wedding photographer – book 30 weddings a year at $2,500 each, that's $75,000 gross and I think it would be hard to get 30 bookings in a year (especially here in the Midwest). Plus, that's only wedding photographers, which is about the only remaining market today. That's a gross figure, and doesn't include any overhead (advertising, materials, equipment, assistants, etc. etc.)
Maybe some of the pro photographers can enlighten us.