Quite sure you are speaking about iPhone 4S or iPad 2. I'd like to inform you those are old devices, slow also with iOS 7
It doesn't matter what device it is. If a 4S slows down with iOS 7, Apple surely knows that, and can inform the customer that is 6 is the optimum operating system for that device.
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Sure, unless the developer forces your hand.
Skype and Yahoo Mail apps only work on iOS 7+ now. Sucks to be whoever is on iOS 6 and needs those apps but don't want to upgrade.
I do agree with you. That will have to be the price to pay. I ran my iPad 3 on iOS 6 for 3 years. There were a few apps I had to pass on, but I'd rather good performance and miss out on a small handful of apps.