Thanks Otto, that post is much appreciated :)
You seem to be misinterpreting how it is beneficial I suspect.
Shorter URLs are easier to remember, hence better for SEO. It doesn't matter if you have
http://domain.com/?p=4 as a shorter version as most people will be looking at the pretty permalink and so they're more likely to remember it if it's pretty and short. Pretty and long is hard to remember, ugly and short is hard to remember, pretty and short is easy to remember. Remembered links are more likely to be linked to in the future and require less "dragging" to copy and paste so are more likely to be linked to as well, therefore pretty short URLs have potential
SEO benefits. Maybe not a lot, but to say there aren't any (due to these reasons) is incorrect. There may or may not be
SEO benefits in having other words in there, but that's a separate issue in itself.
Which is all academic as the difference will be relatively negligible.
At some point I'm now going to have to change my permalinks and make sure everything is pointing the correct direction again :(