Agreed with Cirno!
The flip screen hinges have been an issue with younger users. Once they break, the system doesn't operate.
I also think that the $40 price drop from the standard 3DS is being trivialized. You cannot buy one child a system and not the other. Families with several children may not be able to afford gifting 3-5 3DS's, $510-$850. With the price drop, the costs for the 2DS is, $390 - $650. This is a huge difference as the holiday season approaches in the months following the release.
Lastly, 3DS visuals may be a concern to parents.
All of these elements are what makes this device a good idea.