I believe the missing bit (to allow iOS 4 devices to recognize the printer) is adding the announcement of the image/urf MIME type, plus the URF=W8,SRGB24,CP1,RS600 value. (I suspect that the URF key might not be necessary, but I haven't tried without.)
As far as I can tell, nobody really knows what URF images look like, but right now, all iOS print jobs are submitted as PDF, so it has little relevance.
I believe the missing bit (to allow iOS 4 devices to recognize the printer) is adding the announcement of the image/urf MIME type, plus the URF=W8, SRGB24, CP1,RS600 value. (I suspect that the URF key might not be necessary, but I haven't tried without.)
As far as I can tell, nobody really knows what URF images look like, but right now, all iOS print jobs are submitted as PDF, so it has little relevance.