Idk about Steam but even if that's true, some people bought physical copies of the game not expecting that bullshit. Many were not in countries where PSN even operates. It's bad business for sure. If it needs PSN then that needs to be the first thing you see in the description, like "Now available exclusively on PSN..."
Idk, that's what I heard. I looked around and the standard $60 edition comes with PS and PC versions. I can't say if one of those is digital only, but even if it is some people were not happy campers about the PSN requirement not being advertised. I assume the PS versions of some games can be played offline with no account, but idk. I don't have a Playstation or a PSN account.
All non-free PlayStation games require both a PlayStation Network account and an active PlayStation Plus subscription for online play. Free games don't require a subscription but still require an account as far as I know. And seeing as Helldivers 2 is online only, you need both an account and a subscription to play it at all on a PlayStation.
