Imagine...
Bill Gates: "Hey Stevo! I had some calls from some of our customers. Every time they receive a Word file by E-Mail from a Mac user, they can't open it until they rename it."
Steve Jobs: "Oh. Hmm... Maybe we could add a dot and three letters to our file names."
Bill Gates: "That'd be great! In fact - we could help you with this. We have over a decade of experience (haha, no pun intended) with truncated file names!"
Steve Jobs: "Hey, cool. Send the code over."
...
Some developer: "Hmm, Mr. Jobs, the code we were sent by Microsoft... It doesn't really make any sense..."
Steve Jobs: "Well, we've an agreement with Microsoft. Try using it for a different purpose. If you can't find anything else, use it for something in the GUI for Woz' sake!"
Developer, murmuring to himself: "We could use it for the Icons..."