If they would have put up a banner in the game or a popup every log in stating ..
"Sony account requirement temporarily suspended.
Please note that in a future update this will be a hard requirement and you will not be able to play Helldivers without a PSN account".
Then this would not have been an issue. The question is if their game would have gotten as big as it did. I'll bet 'no'.
Also how fucking lame is the playstation network that they still cannot handle proper game launches.. ffs this should be a non issue by now. The servers that handle this should be setup to spin up and down clones when needed... But nooooo that costs extra money.