The form fits the content. But... always?

I guess this is one of the golden principles in literature: the form fits the content. We then learn that, actually, form is content.

But... always?

In a song like "Yer Blues", by The Beatles, this is clear.

In Suzanne Vega's "Luka" and 10,000 Maniacs' "What's the Matter here", this is not so clear...