g1smd - 11:38 pm on Nov 23, 2012 (gmt 0)

I believe the original spec

hostname is case insensitive. folders and files are case sensitive on Linux systems.

Windows...we won't go there.

older operating systems could only handle three-letter extensions

::cough:: Windows.

Nowadays, you don't need any extension at all on the end of the URL for a page.