Ashlee Vance of the NYTimes puts the cost of developing an ARM-based chip at around a billion dollars for companies like NVidia, Qualcomm and Apple. And that's without the fabrication process to actually produce the chip.
That's quite an investment for Apple and something that smaller companies like Palm wouldn't be able to fund. Apple got a head start on their A4 chip production by purchasing PA Semi for a quarter of that price two years ago, but has likely been spending liberally ever since.
Until the iPhone "platform" was unveiled in 2007, ARM designs weren't considered for processors that could power "actual computers."
