In Bill's defense, I have long had this problem with the Finder. If I create a file in Textmate but assign it no extension, a blank document icon is assigned the file and the default application -- no matter how hard you try to change it through the Finder -- to open the file is always TextEdit.
As many people have pointed out, this is indeed a Finder problem, but it makes it no less frustrating for users who do not wish to have extensions on text files. (In the old days, wasn't that what the resource fork was for? And wasn't the promise of the modern OSes to dispense with the file extension system?)
john