I still really hate the “+” thing they have to do for Apple Arcade because the store doesn’t allow two apps with the same name and you can sell a game and also have it be a part of Arcade… just so weird.
Most games released with a plus have some new features or modes. In app purchases are not allowed for arcade games. I got it because the bundle with iCloud storage and Apple Music is a better deal for my fam, and though I don’t game a lot on my phone, it’s nice to know I won’t encounter scam micro transactions when I’m trying to fucking relax.
I think for some cases the app already in the App Store has ads and other monetisation (e.g. IAP). In these cases the app is modified to remove these and allow you to get the benefits that were behind a paywall in-game
It’s been on the regular App Store as a paid app for ages as well. This is for subscribers of Apple Arcade, who now get it as part of their subscription.