Why did Palm spoof the ID in the first place? Answer: Because iTunes would only talk to devices with a certain vendor ID. Blocking communication based on vendor ID is also a violation of the USB standard.
The purpose of USB is to be open, and compatible. Any use of the USB spec contrary to that is against the spec. As I've said before, the correct approach is to use special commands in the communication channel with the device to determine if the device seems legitimate, or some kind of encryption key passed through the communication channel. But not USB ID codes.
Blocking devices(or allowing certain devices) based on ID is against the spec, same as spoofing IDs. IDs can't be trusted if everyone is running around spoofing everyone else to maintain compatibility. That's the reason for both rules in the USB spec; if everyone follows the first, no one has a reason to violate the 2nd.
Like the quote says... great artists....