In a CMS you typically have content components that don't really
meaningfully show up anywhere on their own other than within the CMS
itself (like stock images for example). Also, content producers and
editors probably want to have a flat view of existing articles,authors
etc. rather than digging through the heirarchy defined on the public
side. And finally, where something ends up being placed on the site
may not happen until well after the content item is created. It's
easier to implement a sensible presentation layer for content
generation by having folders organized by content type and then
mapping them into the site map
I think that was the thinking behind divorcing the CR heirarchy from
the site map (well that and it was developed by the rebel code
conclave).
Look at etp now. I would like to see all the etp pages, when were
they last updated, are there unpublished revisions, etc. but right now
it's extremely site-map-centric. You have to know where where in the
site to look to find pages and there is no easy way to reuse content
components.
Of course etp solves a deliberately small problem and does not claim
to be a general CMS for content generation and it's certainly possible
to be site-map-centric and still cater to the workflow/UI you would
want for publishers and editors but there seems to be a tradeoff
between simplicity on the content presentation side for simplicity on
the content generation side and I think the later might be the more
difficult to address.