"Clever" developer limitation like this almost invariably cause developers to come up with even more convoluted solutions to problems than needed. Don't disagree that long functions can be an indication that someone was copy pasting a bunch of stuff around in the codebase, but not always!
Obligatory Hank Hill. I'll tell you hwhat. I've seen some poorly structured code with nothing but small functions. Like a state machine implemented via chains of callbacks that could all just live inside one big switch statement.
Reminds me of Carmack on the benefits of long functions: http://number-none.com/blow/john_carmack_on_inlined_code.htm...