AVRCP 1.4 is basically a superset of ARCP 1.3 and so is compatible by definition.
The problem probably lies with the implementation of BT 4.0 in the software iOS 6 and hardware (iPhone 5, 4S) in use.
BT 4.0 is compatible with previous BT standards (e.g., BT2.1) but only if the BT drivers correctly implemented the earlier standards. As is now being found out not all BT drivers were correctly implemented and some are now having problems with BT 4.0.
Slowly, the vendors Kenwood, Pioneer, etc. are correcting their firmware and releasing updates to correct the problem. You will have to wait.
Arrogance is not an issue.
Shouldn't Apple test the new version before it is released? Do they even test it with existing third party hardware? And then claim that the third party vendors, did not implement it correctly? This is exactly what Microsoft used to do, and still continue to do. Before releasing the AVRCP 1.4, Apple should have notified the third party vendors on the upcoming change so, they would start working on firmware upgrades. They don't like to inundated with irritated customers calling them with complaints.
As a consumer, all I know is it used to work in iOs 5.1.1 but does not work when I went to iOs6...so the problem is with Apple. Kenwood and JVC have been very responsive and they said they are working on a solution, but do not have a timeline on when the solution will be available.