IMO that presents an opportunity: If 1:1 throughput isn't possible given the platform, what are the different ways we could approximate it? If we have to do design in advance, how much should we do, and which parts? All of these become useful challenges that can increase the role of feedback in your design when you take them on as such.
I work with some amazing designers and some amazing iphone hackers, and it still takes a team of four programmers a whole month to implement something that a designer comes up with in a week.
Maybe eventually the tools will improve, but iPhone and Android are not web enough to be so rapid.