AirNoServicesAustralia DirtyPierre
In the UK inclusion of the word "heading" is not really overkill. UK ATC use headings to separate traffic to a much greater degree (no pun intended) than any other ATC provider in my experience. Since the R/T is almost always very busy, inclusion of the word degrees helps to pick out the purpose of a three digit number amongst the many others which form an almost continuous stream.
The term "millibars" is added primarily as a hint for US operators. I am surprised that you guys don't feel the need to add the term in Oz, because I don't think it would be an exageration to say that at least one US pilot every day will fail to readback his/her clearance in a way which convinces the controller that he/she is climbing/decending to an altitude (as opposed to a flight level) and has set the QNH.
This is NOT meant to offend US pilots, I am the first to admit that I struggle to switch my mind to US phraseology when I fly over there and hence make mistakes. Use of "millibars" is just UK ATC's way of adding an extra level of safety for operators who are not exposed to European ATC methods every day.
Just my ideas on the matter
G W-H