If you are living in the US, you’ll see the Itunes App Store list prices of apps and in-app purchases in USD. If you live in Australia, you’ll see it priced in AUD, and this is more or less the standard practice for apps for most parts of the world. However there are some countries in which Apple has relied on USD.
However that has changed because Apple has since updated the Itunes App Store to now display local currencies for 9 countries around the world. This includes Egypt (Egyptian Pound), Kazakhstan (Kazakhstani Tenge), Malaysia (Malaysian Ringgit), Nigeria (Nigerian Naira), Pakistan (Pakistani Rupee), Philippines (Philippine Peso), Qatar (Qatari Riyal), Tanzania (Tanzanian Shilling) and Vietnam (Vietnamese Dong).
This means that if you are from those countries, prices for paid apps will now be listed in your local currency. As for developers, they will also get paid based on the local currency, although given that currency does fluctuate every so often, it means that you might not always get the same rate as before.