There is no doubt that the emphasis in Espoo has not been in UI performance, I remember reading a Nokia engineer saying that until the the iPhone launched they had never placed any emphasis on 'smoothness' in the UI only functionality. Symbian foundation realizes that UI is now the selling feature (IMHO moreso than apps) for launching a new device and so this delay must be to iron out issues and deliver a worthy product.
Nokia isn't going anywhere soon but they really only have a couple of years to turn things around in the high end smartphone category that they defined for many years.