Originally Posted by fratts
The main reason is the transfer speeds between the application memory is much much faster than the speeds from the SD card. If they allowed users to install apps to a memory card, the performance of the device would probably be horrendous, at least while accessing those particular apps.
Not if they cached it into memory while running. There'd be a momentary pause when starting the app, but none while running.
This may increase memory footprint of running apps from card, but by saving memory of many apps, more apps can be loaded. So many BlackBerry Bold's are still in use today, and they run out of memory much more quickly than the newer devices, when installing a few apps from App World.