gee wizz.
I am sure, and I say this because it seems the most logic explanation, not from any research on the matter, the word lyric was created to give the words part of a song a title, just likie the melody was given to that part of the music.
I would agree a lot of the lyrics on any forum may never see the light of day as part of a done song.
But I do believe a lot more of them are doing so because of the fact we do have places out there we can put our lyrics up in the hope a composer or two may hear them being sung enough to add the noise and stir.
Look on the MP3 forum and see how many of the lyrics do in fact make it to being sung.
Quite a few.
SongRamp with its writer's Room Forum, although way less active than JPF lyric, has a very high percentage of the lyrics put up there making it to being sung and showcased on Open Mike there.
Likewise, their Music Seeking Lyrics has a not to be sneezed at number of completed songs come out of it.
If it is sung, it is a song, no matter if the words were a poem or a lyric originally.
Graham

http://www.soundclick.com/bands/2/grahamhenderson_music.htm