"failed to exceed their expectations"
Just wait until it's released and 3/4 of Japan start selling their grannies to get one. Every iteration of the DS (whether it be a hardware upgrade, special edition or new colour) has had a major boost on sales. I see this being no different.
Sure it's not a great imrovement over DS, but it's not DS2 - why should Nintendo give everything up so early? Why not just add a few touches to the original and remarket? The DS has plenty of life left yet and the DSi will only extend it. When that starts failing, Nintendo will release DS2. It's how they work.