15 minutes after Macrumors updated their front page post, saying that Apple had replaced the previews with the earlier iOS 8 and iPad Air (1) images AND on my iPad I could see that the images had been replaced, I decided to take a look via my iMac. Indeed the pictures were back, showing the iOS 8.1 guide with iPad Air 2 and there was _no way_ that these images could have been cached on my iMac.
This has to be a deliberate attempt at drawing attention away from the big-G and get people talking about the new iPad(s). Why would the images have reappeared otherwise?
Although, saying that, when I updated my iBook via iTunesConnect some months ago, even though the updated book was sat in the queue at Apple for verification, iTunesConnect allowed me to update the screenshots to those from my updated version, meaning anyone buying the book would see new screenshots and got an older version of the book until the update was released - so I can understand how this can happen without the person doing it realizing.