Your renter pays the market rate for rent for that property (in general). In your case, that happens to work out in your favor. But in a place like SF, a 2 bedroom apartment costs $1.5 million, which is ballpark $7k+ a month. I can rent a 2 bedroom for less than half that because the market is simply not paying $7k a month for 2 bedroom apartments.

I've also rented a house where my rent payment did not even cover the mortgage (I knew the landlords - they had bought in 2006 and were still waiting on the market to rebound so they could cash out and move on).

So as the article says - it all depends.