> [1,10,5,-15,-2,4].sort(function(a,b) {return a > b})
    [ -15,
      -2,
      1,
      4,
      5,
      10 ]
    
    > [1,10,5,-15,-2,4].sort(function(a,b) {return ""+a > ""+b})
    [ -15,
      -2,
      1,
      10,
      4,
      5 ]

Perhaps .sort was initially designed to do something else, like sorting strings, rather than integers.