Why does Apple's Earphones with Built-in Mic not work on computer?

Buds4_medium

So I can plug Apple's earphones with built-in mic into the headphone jack of my iPhone/iPod normally and be able to listen and talk on it. Why does this not work when I plug these same earphones into my computer and have them act as both the speakers and microphone? I've tried plugging into both the speaker jack and the mic jack of my computer, and the built-in mic does not seem to work.

More of a technical question; hope someone can clarify for me. Thanks in advance