To be fair, it’s heavily implied that the Stormtroopers were missing the heroes on purpose specifically to lure them into a trap in Episodes IV and V (specifically, to trick the Rebels into guiding them to their hidden base at Yavin IV, and get them towards the Executor).
Besides, I’m pretty sure the Empire wouldn’t have lasted NEARLY as long as it did if they were extremely bad shots (Obi-Wan and even Leia implied that they were crack shots).
Wasn’t expecting that to draw a reply after 8+ years. :)