The bulk of super hero prose tales seem to coming be from independent publishers.
Is this a way getting around the "can't afford an artist" hurdle that keeps many
out of indie published comics, or is there more to it than that?
I believe that we have a generation of writers who grew up loving super heroes and they've realized that they have the ability to tell stories about them with an unlimited special effects budget in the pages of prose tales. They also have learned that there are stories that can be told in prose that just wouldn't work in comic book pages.
As I said in one of my tutorial about writing a few years ago, a picture may tell a thousand words, but sometimes a thousand good words can tell more than a picture.