The short answer is: 'No'.
The constructive answer is: "try it and see".
The pedagogical answer is:
The first one adds two key=>value pairs to $array. Assuming $array is empty to begin with, it's equivalent to
$array=array(
'key'=>'thekey',
'value'=>'thevalue');
which is nowt like the second example.
(and you should've said $array['key'] when writing the first example)