Dave Winer : Another way of looking at it -- RSS is great for news, but not everything is news, some things, like the distance between the Earth and the Sun, or the elements of the periodic table, don't change. Or change slowly, like the teams in major league baseball, or the top home run hitters. For information like that, knowledge, representing the relationships between nuggets is
what's important, and that's where outliners like the OPML Editor, that's now in beta, excel.

www.podcatch.com :

OPML is dynamic like RSS. But is intended for a slower shearing layer

Fast changing news is a line. Slower changing facts might be a tree[1].

[1] Though not all knowledge is a tree, of course.