I have had the opportunity to see lenses from photojournalists. My glasses are cleaner then most of them. Now granted newspapers are probably more forgiving in print than other things. But man it blew me away. I don't use protective lens filters but use lens hoods instead. Don't seem to have a problem with scratching and I am brutal with my equipment.
Now as has been mentioned. The sensor. A totally different story.
Greg Luer '85 4Runner, '89 FJ-62