Melchett, that was my understanding too. For promotion you needed a bunker tour which of course got you posted from the E3.
When I was at Tinker they were recruited as AWAC crew and considered themselves as aircrew. One reason could have been the declaration that there was 'no air breathing threat' to ConUS and thus no need for an Air Defence setup; got that one wrong.
In the UK, given that the number of airborne seats is very few the gene pool would be too small to follow the USAF route; bit like the WSO(Nav) pool which is rapidly drying out.