I read that too, with a grain of salt and subsequently did a 'find . -name "*er.java"' just to see. 23 out 148 matched in one of my projects. Cursorily, half of them are nouns and the other half are a combination of Loader, Manager and Handler. :)

I think its more a case of doing what I've seen done before. Maybe some "angry monkey" but maybe more like "Hey, that seems like a good way to do it."