> Yet it's quite likely you'll interpret someone promoting a work in the comments section of a site you frequent as a friendly recommendation
The difference is intent. People directly advertising in comments get downvoted, promoting something relevant as a friendly favour are upvoted, and people doing the former while pretending to do the latter are considered sleazy bastards and subject to being pruned from community if it is to stay healthy.
The difference is actually subjective gauging of intent. Particularly your latter case of the "sleazy bastards" is often an intrinsic gray area and of course in the best case indistinguishable from a mere recommendation without special interests.
The difference is intent. People directly advertising in comments get downvoted, promoting something relevant as a friendly favour are upvoted, and people doing the former while pretending to do the latter are considered sleazy bastards and subject to being pruned from community if it is to stay healthy.
It really is simple. It's about trust.