You are right, there really aren't any differences. The only difference I can detect is that the N220 is slightly lighter, but otherwise than that, nada. My guess is that one model is for one part of the world, i.e. Asia and the other for the U.S. and North America.
I recently bought an N150 for traveling. Absurdly great battery life.
Hey, did you know that if you have Win7 on it, you can hotkey [Cntrl][Alt] [Left or Right Arrow] and rotate the screen 90 degrees? Makes a perfect ebook reader. You can hold the thing sideways like a book with your thumb on the Page Up & Down keys.