Not to mention that Apple's support for the PA6T ends next year and they can finally bury the chip. Apple's prime focus has been on the A4, A5 (and A6) chips that power iOS devices.
If the chips do indeed cost £400 (US$650) that's a big pile of money for only two cores running at 1.8 GHz, 4 core Xeons can be had for a third the price, as can quad core i7s. Both running at over 3 GHz.