Hi Ryan,
I have never played around with this. However, when I was working on this:
http://forum.arduino.cc/index.php?topic=146574.0
I added the notes in the attached picture Capture.png.
Component highlighed in Capture1.png.
Why would they do this?: It makes the board easier to use (consider the market). Also, Vref can only get smaller than this current value. By fixing it on the board, I suspect that they hoped to reduce failures due to folks applying 5V, and the like.
Regards,
-Chris
