[jaimebuelta]

That's because, most of the time, a keyboard/mouse will NEVER be cleaned (and desks themselves something like twice a year) while toilet seats will be cleaned quite often, even more than once per day in a big enough office.

I clean my keyboard and mouse regularly, as well as try to keep my hands clean while I'm working (if I eat a chocolate, I'll wash my hands afterwards, for example), but I know I'm the exception.