I am not familiar with the UK postal services and cannot comment. What I do know is that I quite often order from large as well as small UK on-line stores and delivery charges are very reasonable. Somehow they seem to manage that.

You were horrified at the cost to send something to the UK and wondered what it would cost to send it from the UK to Australia.  I looked it up for you and found that it was more expensive.

You do not need to understand anything....the Royal Mail website works just the same as the Australia Post one and the USPS website for that matter.

There is no point in complaining about Australia Post if you are not prepared to do your comparisons and see that they are just as competitive as other services the world over.

As for reasonable delivery charges from other on line stores....have you ever thought that they may be subsidising their delivery charges.  Have you ever looked at the actual postage on the packet as against what you were charged?