that's the rumor. it's also possible that dropping it in the beta showed them that it was popular enough that there are risks of server overload. i still remember the crashing of iCloud when it was launched with the new iOS on release day. last thing they want is a repeat of that. even just iOS and a new device on the same day is bad news, thus why they are releasing iOS 12 4 days before the product launch. get past the initial big wave of activations and then add the nifty new trick