> For reasons I don't remember, the Perl interpreter allows arbitrary code in the inner "[...]" expression that creates the array reference.

...because it's an array value? Aside from how the languages handle references, how is that part any different from, for example, this in python:

  >>> [5 * 'x']
  ['xxxxx']

You can put (almost) anything there, as long as it's an expression that evaluates to a value. The resulting value is what goes into the array.