There are plenty of industry reports and infographics that give us an idea about the state of Apple's App Store. Apps are being sold at an average price of less than $2.50 each, and there is speculation that app sales could be a $34 billion dollar industry by 2014. In 2010, iOS users spent an average of only $4 each month on apps.
I have a feeling that the user statistic of $4 a month is a product of the way that averaging statistics bend numbers. There is still a huge divide between what most would call "power users," and the "average users" of technologies like the smartphone. (If you read iDB, most likely you're a power user.)
There are people that are really into buying and trying different apps, and those people purchase a lot of apps. Then there is the vast sea of average, mom-and-dad iOS users who may download a free app every now and then, but don't make money purchases in the App Store too often. The good news is, you can easily see how much you're spent in the App Store with a nifty utility for Mac OS X...