while I buy digital music on a regular basis, I still love the idea of CDs- something tangible that gives me more than just the music - liner notes, pictures, lyrics, all the writing/production credits etc. There’s no doubt in my mind that the advent of digital music has devalued music and the consumption of it. Quantity has overtaken quality in many cases - how many free songs can I download, how much can I fit on my iPod, how many new artists can I find today. Nothing inherently wrong with any of that, but it just means that, in these terms, a single, solitary song is seen as disposable and barely worth paying for.
1) Additional SEO-able content for your site
2) With the addition of comments, you can create community around one song and further engage your audience.
3) Adding all this value for one song adds an additional emotional appeal to your music. Not only can fans see the amount of care and attention that has been invested on the part of the artist but it broadens their experience of the song and their emotional attachment to it.
4) By using a Creative Commons license and encouraging derivations, the life of the song is extended.
What I take from this is that it gives reasons why musicians and their designated rights holders would want to create dedicated pages for songs. Given that you've invested in a song, you can enhance the value of your investment by giving it a page. The situation is a lot like music videos, except that the content type is anything that goes in a web page rather than strictly moving pictures.
The comparison to music videos is natural, and it gives a simple explanation for why you'd give a song a page. In the old days television was the medium for culture. These days it's the web. So the existence of song pages is a straight transcription of music videos to the new medium.
But this way of thinking about song pages is in opposition to the perception of song pages as packaging. Are song pages more like big-ass gatefold albums or music videos?