Because Microsoft don't like any of us?
Seriously though the only explanation I can come up with is a possability and I hope you don't me having a guess.
Office is designed to be intergrated so that the parts work together you can import an item from one part of it to another part if you follow and its POSSIBLE that thats why it comes up with these updates IE because its needed to allow the integration between the various parts of Office and the update can't tell which version of Office you have.
Actually after typing that and thinking about it, it seems to me that the most likely explanation is simply that it can't tell which version of Office you have and gives you all the updates.
I have no idea if either of those guesses are right but its a reasonable supposition.