As for acetone being hygroscopic, I believe that' true. We used to mix 50/50% water with acetone for anti-knock water injection on supercharged engines. It would mix thoroughly into a solution.

But, I thought methyl alcohol was also hygroscopic?

I'm of the same thought about acetone as Shotgunjones, acetone being highly volatile and leaving no residue of consequence. But I still like to leave an acetone soaked stock dry a while for dispersing the acetone out.