Actually, 250AUD is pretty much exactly 250USD. But remember, FX rates are spot rates, they don't take into account the FX risk incurred by holding money over time in the foreign currency. So it makes sense to for a US company to charge a premium to customers using a different currency. (Note the forward prices vs. spot for AUDUSD here: http://fx.sauder.ubc.ca/closing.html)
Besides, by the time you pay for shipping and tax in New York, the $199 tablet is $232!
I get the next worst result - the $200 tablet would be £130 at current exchange rates but in the age old tech rate-of-exchange it's £200. An apparent ~50% markup is a turn off.
The 8G tablet is only £159 in the UK, or £132.50 before VAT (US prices typically don't include tax). That's about $205 at current market rates, which is as close to the US price as makes no difference.
Surprisingly, the UK is getting the same deal as the US this time round.