Hi NHAH
As several people have said, the term 'window-washer' is often used to represent individuals such as elders who have an anti-education stance, while having influence over people's lives in roles that they have no qualifications or training to carry out. I agree with you that it is unfair to imply that there is anything fundamentally wrong with window cleaning as a career choice.
Through my relatives I met a JW elder (he is in fact a window cleaner - sorry!) who told me that he didn't believe in evolution. When I asked him which books he'd read on evolution he said he hadn't read any. I offered to lend him some but he declined on the grounds that he knew it was wrong so he'd be wasting his time!
He may be a great window cleaner, but his critical thinking capacities are clearly very limited and it's painful to think that he has a lot of influence at the KH.