I've read through the the various threads about the ECU proposal for 2008, and did not come across any discussion about Adjustable Fuel Pressure Regulators. If I've missed it, please point me in the right direction.

Current rules allow the addition of an AFPR. Why does the proposed rule do away with this allowance?

AFPRs are a nice, cheap way of adjusting the fueling. The removal of this allowance would make an (expensive?) aftermarket ECU a must-have option to perform the same basic function as the AFPR.