Apple should let users purchase iPhone apps and run them on their desktop similar to Dashboard widgets.
You should be able to purchase through iTunes just like users do already and then be able to run them on your iPhone, iPod touch, or on your desktop. Apple already has the technology to do this on x86 based Macs already (proof being the iPhone Simulator). By doing so they would open up the market to a wider set of users who don’t use iPhones but wouldn’t mind some addictive games/utilities and other toys. Most of the applications would actually translate very well. The presentation could be similar to that of the Dashboard Widgets. Same size, same functionality. Controlled via a mouse. Gestures would be slightly more difficult to handle but could be managed with an appropriate human inteface API.
Bonus points if they copied the Kindle’s iPhone app’s sync ability so that developers could let their applications stay in sync via WiFi or MobileMe (remotely). Keep your high scores intact between your phone and your computer.