You know what? I'm kinda with Dan on the Skrillix/computer music nonsense. If you don't play an instrument, you're not a musician. You don't get callouses on your fingers from making music on a keyboard. You don't get a tighter, disciplined embouchure from making fucking dubstep. I'm sure it takes all degrees of skill and talent, but you're not a musician.
Then again, I have weird opinions on music. I'm also of the opinion that you shouldn't be allowed to be a lead singer without at least playing rhythm guitar.
I've played about 10 different instruments with decent proficiency in my life and my personal opinion is that if you are playing and/or composing music, be it an instrument, on a computer, by mixing two records together at the same time on a turntable...whatever....you're a musician. Skrillex is definitely a musician.