@Timboli. It is not ethically wrong every time one group of consumers pay a greater price than others. Nor are early purchasers who pay a premium subsidising later purchasers. Where there is healthy competition the laws of supply and demand determine the price, though these forces are of course sometimes manipulated by things like collusion and legislation.
The high prices in Australia are an historical artefact. Australia was given its independence. As a result of this the British were able to retain a lot of the influence and control over their former colony. This left us with some of the highest prices in the world, maintained by mechanisms like parallel import legislation which for books continues to this very day, despite Productivity Commission recommendations. Pricing of various tech products in Australia was the subject of a Parliamentary enquiry. I won't link to the report but to this article which is a little shorter:
Australia Tax
Consumers do have a choice. If the price is too high, don't buy. If you know that the price will drop in the future and be what you term "a steal", but must have and buy it now, you are paying a premium for that early access. This type of windowing works because there is enough demand at the higher price. Of course businesses are going to satisfy this demand before picking up the demand at lower prices if they can. Weak and desperate is no way to describe your fellow readers who choose to buy a book earlier at a higher price.
Ironically enough I agree with you that the pricing of this particular book is too high. Others think it is great value. Both you and I have reacted to this, you by buying a version at a price you found acceptable, me by not buying at all. Give the Big 5 time. They seem to have come to some appreciation of the new reality and are experimenting with their pricing. Unfortunately it makes business sense for them to pick up the demand at the higher prices first, which they have long done with different editions of print books.