Seems To Me Coins From Australia Are More Expensive Than British ? Why?

I am going to hazard a guess...

Population + disposable wealth.

Thinking about it there are a lot of Americans chasing American coins and they command the highest prices.

There are somewhat less people chasing British and still fewer chasing Australian.

Obviously supply is the other side of the coin but in terms of demand it seems logical that USA>UK>Australia

Quite right on your first 3 points, but on your last, collecting interest was not high on the UK mint's priority list.

High grade early Australian trade/merchant tokens are both very scarce and very expensive in many cases.

The Sydney Mint opened in 1855 as a branch of The Royal Mint, followed by Melbourne & Perth, but AFAIK, the first Commonwealth coins were not struck until 1910 or so (i.e. those with reverses unique to Australia); prior to that I think the circulating coinage was mostly British, although an Aussie numismatist might be able to verify that.

In 1921, the Melbourne mint struck 7.3m of threepence, the highest mintage for that series of 3d; by contrast, Britain only struck 8m in the same denomination. However, a mid-range Uncirculated (MS63) 1921 3d can be had for under $40, while the same coin, but Australian, is a $200+ coin (USD.) This implies that there are other factors besides mintage that affect prices, most likely condition scarcity as a function of circulation.

@ Mendelman got it right...about Aussie silver coinage continued to be 92.5% till end of Second World War.

Plus when Australia changed over to dollar and cent system, the Government melted majority of silver coins. This may be why the prices are higher for Aussie coins than British coins.

It is my understanding that mintage of many pre-decimal coins were somewhat lower than they should be for Australia (they do not mint enough coins in some years).

I would have to concur with Finn235 on his three points.

During the Second World War, Australia could not mint more coins so they asked the USA to mint silver coins for them which was duly delivered. After the War, Australia had to melt silver coins to pay back to the USA for those silver coins. I think it was in mid-1950s.