I was thinking along the same lines, but the fact that the following does work seems to contradict this argument, or at least imply that it's not the whole story:

map { $_, 2 } @l;
[download]

Though, now that I think about it, all this probably reflects a perl heuristic/optimization in the parser which says something along the lines of "if, within the bracketed expression, I see a constant and then a comma, I'm going to assume the expression is a hash, and not a block, no matter what comes afterwards...."

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print