State sales tax in Oregon (one of the places I visited) is nil.
It's not just Apple products, either. To give another example - the Antler suitcase, model Novanta Medium. At antler.co.uk, at normal price it sells for £95, or about AUD$152. At luggagegear.com.au in Australia as well as Myers, the same bag goes for AUD$185, or 22% more than the UK - and that's after a supposed "35% discount".
Or how about IKEA's "Markus" office chair, which sells for $399 here in Australia. In the US, the same chair sells for US$199 (half the price!) and in the UK, £117, which is less than half the price of the equivalent in AUD (£117 = AUD$188).
It definitely pays to do some price research and figure out what's worth paying for and where's the best way to get the item you want.