A named hash is associated with one particular variable (although references to it can be created), where as an anonymous hash is refered to purely through a reference, and subsequently must live in a scalar (be it a named variable or otherwise).

Also the syntax you provided is broken with the named hash (for anyone puzzled by the odd syntax) as the dereference is incorrect, what it needs to be is

my %hash = %$response;
[download]

See. perlreftut and tye's References quick reference for a quick start on references.
HTH

_________
broquaint

update: disassociated krisahoch from the dodgy syntax :)