Yes the flush heel cup and kingpin add enough support and response that they aren't really missed. Plus add that today's boots are stiff enough that it really makes little difference as to if you ride with them or without them. I remember riding friend's boards in the mid 90s with the backs removed or cut right down and this another world as far as feel and response go.
I rode a pair of IPO's today on my Yes Pick Your Line. Definately enjoyed it more as opposed to when I had my Cartels on it. I landed jumps (smaller ones) much better and I just ripped through the pow and chopped pow with confidence. I definately like them alot.