The way I understand it, here in the USA, is that commercial use is when a photo is sold to to say Ford for use in a brochure or ad. This type of work requires releases.
If the photo is sold as art though, it's not "commercial". No release needed.
The other concept in play is that when "we" are in a public space our eyes cannot trespass, everything we can see is fair game. If someone wants privacy it's up to them to fence "us" out.
If I step off the sidewalk onto your lawn though the rules change.