The HTTP protocol offers a MIME type. Where does the server get it? In most configurations, it guesses it. Download a RedHat Package Manager (.rpm) file, and you get application/x-realplayer-media (.rpm) mime type. Oops. Why? Because it used an imperfect heuristic scheme to specify the mime type.

Neither the Windows filesystem nor the Unix filesystem offers typing metadata. Resource forks and Windows .rc/.res resource files offer typing metadata inside their encoded contents.

It's just another example when you and I are in "violent agreement" over some topic. Metadata and type-determination methods are weak, and usually poorly implemented. In my case, I just suggested that two heuristics are better than one, instead of ranting that it's all futile unless you have God's Gift to Omniscient Filesystems.