The array is there to cope with the possibility of an unresolvable host. If you try your example above with args like
./pllookup.pl dklghslfhslgshj.com foo.com
the unresolvability of dklghslfhslgshj.com would cause it to die on the first argument, whereas with the array it will just skip that and carry on to the remaining args. To my mind that's a better UX but others may disagree.