At least for the first example, the reason the JavaScript code is so bad is that the CoffeeScript code is equally bad. It repeats an entire for loop for each character code!

Having a concise syntax doesn't relieve you of the duty to simplify your code. Both the CoffeeScript and JavaScript code can be simplified considerably, as several others have pointed out.

In fact, if you clean up the CoffeeScript code like this:

    keyMoves =
        37: 'pan_left'
        38: 'pan_up'
        39: 'pan_right'
        40: 'pan_down'
        187: 'zoom_in'
        189: 'zoom_out'

    document.onkeydown = ( event ) ->
        move = keyMoves[event.keyCode]
        piece[move]() for piece in game_pieces
        the_screen.refresh( game_pieces )

It compiles to this JavaScript code:

     var keyMoves;
     keyMoves = {
          37: 'pan_left',
          38: 'pan_up',
          39: 'pan_right',
          40: 'pan_down',
          187: 'zoom_in',
          189: 'zoom_out'
     };
     document.onkeydown = function(event) {
          var move, piece, _i, _len;
          move = keyMoves[event.keyCode];
          for (_i = 0, _len = game_pieces.length; _i < _len; _i++) {
               piece = game_pieces[_i];
               piece[move]();
          }
          return the_screen.refresh(game_pieces);
     };

And that's a quite reasonable piece of code - nothing like the JavaScript example in the article.

Personally I would write the JavaScript version more like this (assuming I wanted a raw for loop instead of an iterator function, perhaps for speed):

    keyMoves = {
        37: 'pan_left',
        38: 'pan_up',
        39: 'pan_right',
        40: 'pan_down',
        187: 'zoom_in',
        189: 'zoom_out'
    };

    document.onkeydown = function( event ) {
        var move = keyMoves[event.keyCode];
        for( piece, i = -1;  piece = game_pieces[++i]; )
            piece[move]();
        the_screen.refresh( game_pieces );
    };

But I certainly don't see anything very wrong with the CoffeeScript-generated JavaScript, once the original CoffeeScript code is improved.