Bill if you work with a guy and you spend several hours digging over the garden only to see him come along and lay the turf in a few minutes expecting to be paid the same....would you insist on him getting the same wages?
The 50% split applies when someone writes lyrics and someone else whistles the tune......to turn that into a demo requires much studio time...that costs money and the cowriters should split the costs equally even if the person making the demo is a cowriter...he deserves an extra paid for hire for his work.
I have never charged for this demo service however.......despite providing it numerous times. just stating what I would consider fair.
You seem to insinuate that I think lyricists are stupid or second class....that is not the case. I just think that the art of musicating, or composing as some prefer to call it, requires far more knowledge, time, training and experience.....probaly the reason that lyricists outnumber composers by a considerable margin. Whilst I agree that lyricists can take time to compose lyrics.....it cannot be compared to the time spent arranging, hiring or buying recording studio equipment, recording the tracks, editing and mastering a decent demo.
I am surprised you expect the composer to pick up the tab as that sounds very mean to me.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055