Except a guitar fretboard will get oily, gunky, and much quicker than my ceiling (which has never gotten oily or gunky, I might add). I'm not buying it.
Everyone knows that the dirtiest place on a guitar is the fretboard. That is the only place your fingers actually come in contact with the guitar.
The human body is pretty gross, expelling oil, sweat and dead skin constantly and not just on contact. There's practically a cloud of it all around you at all times.
One property of unfinished wood, and more specifically the dried out and occasionally oiled varieties found as guitar fretboards, is that it LOVES for those oils, liquids and solids excreted to stick to it.
Also, you don't touch the strings?