I think you guys are all forgetting something. Apple produces some things in the US and some in Asian countries. It's probably easier to ship to the US, than other countries as we would be closer. It would also be easier to ship to Australia. The UK is much farther away.
Also, since shipping from a foreign company, they probably charge heavier fees upon importation. In the US, the shipments may come from another country, but the company that produces it is not foreign, so our importation taxes are either very small or non-existant.
State taxes, as you have been saying, are not included. Here in Florida, my mouse is going to cost me $73.83. That would be (according to your calculations) AUD$98 and £40.20. The actual prices are AUD$109 and £49. That's not that bad when you take into account the charges of importation.
For some reason my PowerBook came without paying tax, but lately I've had to pay tax on all orders through the online Apple Store. It's kind of annoying
I wish we had something similar to VAT, it was nice going to Ireland and knowing exactly how much stuff cost without having to do any math in my head. Of course the VAT is really high compared to US taxes. It's only 7% here (used to be 6% in my county but they raised it

).
Also, as someone said, we have other stupid things to deal with here that you guys don't, like having our TV censored even though it's cable because the FCC oversteps its bounds. And not to mention our dumbass president.
Someone mentioned that some states offer tax free weeks...just to clarify that's generally for back to school, as far as I know, so don't go thinking it's everything that can be sold. It most certainly doesn't apply to computer products. It's generally for clothes, school supplies, and sometimes things that should be on it aren't, and things that are (like ski equipment) are. And yes, I'm serious about the ski equipment. Ski equipment is tax free in Florida, or at least it was back when I worked in retail during the last tax free week.
This has become too long. Good luck to all in your mighty mouse purchases!