I can see some logic in the Wii U being a poor naming choice, I am not so sure the 3ds is a poor name in the same sense. The 3ds doing poorly seems to be more because they released a relatively weak console, one without games, had their third party developers split between it and the considerably nicer to develop, market and contemplate the size of audience for android/IOS platforms and their own.
Both the DS and Wii were really popular amongs the casual audience (Which is the majority of people). If I was a casual who doesn't bother reading gaming news I would think the 3DS and Wii U are just upgraded versions of the DS and Wii like the DSI is.
Now with the 2DS, 3DS XL and new 3DS we have a big arsenal of confusion to the casuals. DS2 is a less confusing name and automatically signals that this is an entirely new console. But it appears that lame name puns are more important for Nintendo.