I still don't understand why Nintendo is doing this. Does Sony do this with the PS Vita? No. They should not sell retail titles digitally in my opinion. Arcade games.eShop games/PSN downloadable titles, fine, those are actually really cool features to have and I fully support things such as those but in my opinion companies should not sell games over their consoles/handhelds unless the title IS NOT AVAILABLE TO BUY IN STORES OR ONLINE ANYMORE. Then, go ahead, but if physical cartridges or discs are able to be bought, a company should not sell their retail games (something that does physically exist and isn't a download that started as a download) digitally unless they can't be bought from somewhere else as a psychical disc/cartridge.
Though I can understand convenience, like it says, only playable on that 3DS. Why would you want that? You can get a perfectly fine cartridge with the same content, and have it be mobile.
Just my thoughts.