At least not if you can avoid it. Why? Simple. Apple’s pricing will cost you. For example, Mellel currently costs $41.99 AUD on the App Store. The non-App Store price is $39.00 USD. Now that the Australian dollar is worth more than the US, buying it direct works out to something like $37.00.
Unfortunately, while iOS App Store suffers the same disparity, it is more difficult to get around the Apple version of the exchange rate.