The reason it's a #! is only because of one thing: Google. When site operators realised that their (idiotic) use of Ajax for all page content meant that Google couldn't index their site (the other side of the deep linking problem), Google threw them a bone.
Google said that if they use #! in their URLs to control page content Google would convert the URL into a special query string and then (if they made content available at the URL with the query string) index their content.
The reason it's a #! is only because of one thing: Google. When site operators realised that their (idiotic) use of Ajax for all page content meant that Google couldn't index their site (the other side of the deep linking problem), Google threw them a bone.
Google said that if they use #! in their URLs to control page content Google would convert the URL into a special query string and then (if they made content available at the URL with the query string) index their content.
http://googlewebmastercentral.blogspot.com/2009/10/proposal-for-making-ajax-crawlable.html