I don't get why so many people are salty about this upgrade and it 'fragmenting' the user base. Nintendo has done this with their other handhelds. GB to GBC, GBA to GBA SP, and DS to DSi- all of them vastly improved the original system designs.
The GBA to GBA SP did not fragment the market, but it was a big improvement on the original- rechargeable battery, a backlit screen, and a completely new form factor. If you tried an SP when you just had a normal GBA, going back to that was almost unbearable.
They always do at least one big revision that makes a bunch of changes to the handheld. History repeats itself, why is everybody so surprised?