"Why have reasonable AirPlay peripherals failed to materialize? "
Let me preempt by saying I know that BT is cheaper and better (in many regards), but I like the larger range and central control of AirTunes via iTunes over my network through my two Expresses. But a portable speaker system wont get bellow $200 when you can get a BT set for half that? Is the Apple license and hardware that stupidly expensive or is the physical technology that boutique to remain a niche luxury to audio manufacturers? at this rate (2 years in), it's looking like a slow death or soon only Apple will implement it with their Airports. BT continues to win by strength of numbers and buying power.
1. "I was about to make my own." In response to Reply # 0
Using a cardboard box an airport express and a powered speaker.
********** the test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function.