I know you'd like to buy into the crappy scifi pre 21st century and the archaix teachings of your preschool teacher, but the simple truth is space isnt as "empty" as you might think. It's definatly a hell of alot more empty than inside of our atmosphere, but the truth is that there are particles floating around in space, and that man has been actually adding to these particles by releasing debri into orbital paths around earth. One of the biggest problems with satelites in years of late is actualy debri hitting them from previous space voyages.
In short... is space a natural clean room? Yes! Is it completely clean? Far from it. Something to also consider is that outside the earth's atmosphere, anything is subject to rays of energy that would otherwise be bounced off the atmosphere. A sensitive material might not hold up so well.