Audio files on SD card are segregated from the main device. Why?

“When merging the internal and external memories, I would have thought the limiting factor would be more software than hardware. Sansa already has the code to do this -”

The Clip sport and Clip Jam use a different processor than the Clip+ and Clip Zip. The processor on the Clip Sport and Clip Jam is much less powerful. The code for the newer players is different. 

The UI on the sport seems similar to that of the Clip Zip, however I’m sure the code to implement the UI is very different.