It is your right to doubt all you want. I actually handled the phone and it worked just fine. So in my opinion it is not the most ideal situation but a 4S will run ok on the latest OS.
So why take a device like the 4S running iOS 5.1 or 6 and cripple it with "ok" performance. iOS 8 sucks and you know it. And if it didn't suck then Apple wouldn't be focusing iOS 9 on stability and optimization.
What's sad here is an iPhone 4S running iOS 5 or 6, and iPhone 5 on 6 feels so much better than an iPhone 6 or 6 huge running iOS 8. YES, its that noticeable.