The app store means

  * nearly zero worry about piracy* 
  * much much easier discovery process for average users
  * much higher purchaser confidence (due to b and c)
  * lower purchase activation energy
 

All of these together mean that apps which traditionally scraped by as shareware, thrilled if they got 5% conversion, can now just sell at an impulse-purchase price of $1-5. Larger professionally-produced titles, like games, that have always had problems with piracy, no longer have to overcharge the people who do pay in order to compensate for those who would have paid, but didn't.

*: Part of this analysis is based on the assumption that if the app store DRM gets cracked (likely), the procedure is sufficiently unpalatable that it cracking is not widespread. There are a large number of pirates of convenience out there, who if faced with an app store where what they want is noticeably less expensive than it was before, might decide it's not worth the risk/bother.