This is a very interesting discusssion. I tend to agree with Polly. IMO lyrics without music is just a poem. Melody without lyrics is just a tune. Even the two together make just another song....
To turn that into a hit or even a decent demo it takes great performances and production.
Most of todays hits are production driven rather than performance. The lyrics and melody of today are of little consequence to the overall song.... most modern pop hits have melodies that are very simple and basic most pop lyrics are repetetive almost moronic.....it is the production that makes it a hit. Most people do not even remember the lyrics or even sing the melody BUT are hooked on the production and its gimmicks.
I feel that the production teams in this world are very much under valued and under rated.
They are really the ones who deserve the credit for the song as their work is what really makes it a hit.....not to mention the many hours spent arranging and mixing etc. Probably many more hours put in than the lyricist and composer.

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