Oh... So many questions... Which one shall I answer... Ah! I know, I'll answer them both...
Why is the sky grey today?
I know! It's autumn and when the sky is grey all kind of thingies are happening in the air and stuff... And it's clouded too, which doesn't help either! Now that was a great answer, wasn't it? :P:
Why do we use the word "why" for why and not some other word like, say "what" for why and "why" for what?
Because otherwise "Why are you here?" would be "What are you here?" Doesn't really sound nice ;)
Why (or what) am I in such a posting mood?