Basically, the less apps cost, the more iPhones Apple will sell. It makes the entire ecosystem more attractive to consumers because they know there's 100's of thousands of apps they can buy for < $5.
Imagine how much less your mom would want an iPhone if she scrolls through the App Store and finds mostly stuff that's $20 or $30. The platform becomes too expensive for casual users, who are 95%+ of iOS customers.
Apps are complements to the iPhone and iPad. Spolsky has a great post about the competition between complements here: http://www.joelonsoftware.com/articles/StrategyLetterV.html
Basically, the less apps cost, the more iPhones Apple will sell. It makes the entire ecosystem more attractive to consumers because they know there's 100's of thousands of apps they can buy for < $5.
Imagine how much less your mom would want an iPhone if she scrolls through the App Store and finds mostly stuff that's $20 or $30. The platform becomes too expensive for casual users, who are 95%+ of iOS customers.