i think the biggest thing people are ignoring about the spec differential is, diminishing returns.
it just might not matter all that much, because 1.2 tf and 1.8tf may not look much different at all.
nothing shown as "next gen" so far, gameplay, has wowed me that much. period. not shadowfall, not bf4, not second son GI screens. hell metro last light pc is just the latest "good, not great" looking high end pc game down the pike imo. to say nothing of crysis 3.
maybe we'll actually see more impressive stuff at the durango reveal ironically, to change my mind.
but i think it's an undereported possible angle that, MS may have chosen to forgo spec wars, at exactly the right time. exactly when it no longer matters that much, and things like say, price, where durango should have an advantage, are going to be king.