Simon Willison has a good write-up about the importance of unambiguous URLs, i.e. “that any logical piece of content should have one and only one definitive URL, with any alternatives acting as a permanent redirect”.
Simon gives a good example of how the exposure of one particular site is diluted within a social bookmarking service because its home page has four different URLs. Making sure that a resource has a unique URL has other benefits, most notably in facilitating site statistics and traffic analysis (although most stats packages will provide some way to aggregate "default" index names, aliases and missing trailing slashes, which in a way tends to hide the problem).
This is webmaster trivia, and — besides making them readable, reliable and hackable — good webmasters will knock two birds with one stone by also making their URLs cruft-free, hiding whatever technology they're using under the hood (and making everybody's life easier for future site redesigns or evolution).
(And, of course, I'm not applying the advice here, yet. www.padawan.info should redirect to padawan.info, I'm just getting lost at my own Apache redirect maze :p)
Great point on stats packages - I'd completely forgotten about how frustrating it is to make sense of stats for sites that have the same content in multiple places.