Actually, I'm rather fanatic about washing my hands and keeping my nails manicured. But, not everybody is that way. I've picked up guitars in music stores that were supposedly new that you could tell had been played by people who were somewhat less fastidious about such things. Then, some used ones I've picked up have been absolutely disgusting. I get instruments in here for repair/setup that I'd hate to put under a microscope for fear of what new alien life forms I'd discover.
It's just normal, really. It's not that people pick up their guitars after eating fried chicken and barbecued ribs by hand without bothering to wash. But, skin cells slough off, oils accumulate, dirt/smoke/humidity sticks, etc. The problem is more of a maintenance issue than anything else, and some things are easier to maintain than others.