Unless I am misunderstanding, this isn't true. After I loaded iOS 8 I was able to sync my iOS 7 backup to receive all my settings and apps that I had on iOS 7.
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If you are trying to RESTORE your device to DOWNGRADE from iOS 8 to iOS 7 you need to put your device is DFU/Restore mode (youtube it). Then you should be able to sync your iOS firmware without any problems.