Re: 47 different state sales taxes
Depending on which state you live in, it is the purchaser and not the vendor who is liable for payment of sales taxes. Thus Amazon can collect or not collect at their discretion and if sales taxes have not been levied then it is up to the purchaser to add up all of the taxes they have not paid (by, for example, buying something in one state, county or town) and actually using it somewhere else.
I know this directly as our accountant was slapped with a bill one time for "estimated unpaid state and local taxes", but - being an accountant - was able to document the actual amount owed and it was substantially less. She warned us and we then tracked all out of state purchases. My wife still does the books for her sister and reports "use tax" (basically the difference between what was paid on the item where it was bought and the applicable rate where the item was used) to the relevant tax authorities.
Bottom line, Amazon don't (always) handle US state sales taxes and they certainly don't levy Canadian HST on purchases delivered from the US - even though orders are placed through Amazon.ca. Amazon.com doesn't deliver to Canada (although Amazon.co.uk does). What they have done in Australia is not any different from their policies elsewhere.