About friends and not so

Tell me please comrades Internet users - why the term “friends” is used on almost all Internet projects using social mechanisms
and even forced to become "friends"?

For example, on our own Habré - to write a personal message to a person to report on his mistake, redeem on the sly :)) need to beg for him as a friend (otherwise). I wrote and got back into trouble :). To read posts in communities and blogs LJ - you need to become their friends (you must - I'm already friends with the communities). There are a lot of people with thousands of friends who are openly placed. liveinternet sends a message that they included me as a friend (although I still haven't registered there at all). The only one of the largest communities where I registered and it seems that they did not impose "friends" on My circle.

Why it is impossible to use other terms and force to become "friends"? Why for example non-subscribers?
')
UPD: There is a lot of talk about the need to improve the usability of sites - please consider this psychological point as well. For many, this trifle causes some discomfort.