Expectation of privacy and permission to use one's likeness commercially are two separate things. Releases have to do with the latter, not the former. In a public place, you can take a stranger's photo till the cows come home. You can put the prints in a gallery, book, or newspaper, and even make a profit off of their sale in these venues. But you may not make a billboard to sell milk out of the photos.
Release or no release doesn't have to do with where you are photographing. It has to do with whether of not the images will be used commercially.
Prints in a gallery or fine art book do not need them, even if being sold, as they are art (photos that stand alone as photos), not commercial photos (photos that are used for the purposes of selling/promoting something else).
News photos do not need releases, as the photos are considered as being in the public benefit (i.e. educational/informative).
When you need them is when the images will be used to sell something else, not the photographs themselves. That pretty much defines commercial use. Releases basically allow the person's likeness to be used to make money selling something other than the likeness itself. They say, "You can use my recognizable image in perpetuity to sell whatever you want."
But people don't need to give you permission to put their mug in a newspaper or gallery, or to use their likeness for any other purposes where the point of the photo being published is for the sake of the photo itself. It is when you use a photo as a tool to sell something other than the photo itself that it becomes commercial.
You need property releases as well, for recognizable properties. For instance, you cannot sell a stock photo with a Disneyland ride in the background. (And they will come after you. They came after the children's hospital where I work for making Mickey mouse head waffles for the sick kids.)