Does a File Extension Always Point to a Given Program?

Are there exceptions to the Extension = File Type under Windows?

Many.

With no official registry of file types there is absolutely no control over which program may claim which extension. Also, some programs allow you the freedom to name a file anything you want so long as you place them in a particular directory/folder.

While there is no "creator information" in Windows files ala the Macintosh, a few programs attempt to analyze the structure of a file and if that structure is recognized open the file. You can demonstrate this latter by an experiment with Microsoft Word

• Start Word.
• Type a bit of text.
• Save the file with a strange extension in an easily found directory (e.g., \My Documents\TEST.ASEVES).
• Exit Word.
• Look in My Documents. You should see a file names TEST.ASEVES.DOC with a Word icon.
• Right click on the file and rename it by removing the .DOC extension so the file name is now TEST.ASEVES. [Note: If you can't rename the file with a different extension make certain that common file extensions are set to show. See the FAQ here for instructions.]
• You will be asked if you really want to do that. Confirm the change.
• Windows will change the icon to the icon used for files Windows does not recognize.
• Double click on the file and watch as Word magically starts and opens the file (even after a restart).

By this you can see that Microsoft is starting to build code similar to Apple's creator information into their operating systems. (Of course, for now it only seems to work with some Microsoft products.)