Please define 'casual'

Is the NintendoDS retro ? will it ever be ? the question raised on twitter. Thinking about it, how it was launched and how different the titles available at launch were from other now-definitely-retro consoles (including SNES, PS1, and even GBA),
I'd say the NDS will have harder time to feel retro in general (although some games certainly will). The reason is that, by the time the Nintendo DS came out, the kind of games we played had changed significantly. GBA games play much like slightly simplified versions of SNES games all over the life time of the console. And they play themselves much like more refined versions of the NES games. The reason for all this is the controller.

To me, holding an SNES controller is a well-known feel. I don't have to think about where X or A stands. It is immediate. And it definitely wasn't the case when the SNES cames out: SMW gave me a hard time compared to the 1-button + dpad games I was used to (okay, I pressed SML B button from times to times). And for most games on those devices, it was frequent that you'd need to train yourself to the core mechanics and grow your controller skills before you could proceed further than world 1.

The DS, instead, came up in the world of casual games. Not games that you happen to play casually (as opposed to competitively), but those explicitly designed so that you don't really need training to experience their core gameplay. Zoo Keeper, for once, perfectly fits that line of titles targetted at bejeweled players. They're built around more intuitive and direct actions (thanks to the stylus). Any grown up can start playing them even when they have almost no training with gaming devices. They don't require players to know that they should hunt for 1-UPs or stock power-ups if they want to stand a chance against the end-of-world boss. Really, these are games that Hudson Hawk could have enjoyed despite he's been in jail since Pong is out.

That doesn't mean that there are no retro-like games on the system, but they were pretty rare gems compared to the avalanche of stylus-driven titles. And chances are that the youngster who had a DS as her first gaming system will have nostalgy towards titles that no longer plays like a DPAD+buttons retro game.

Will the NDS ever be retro ? of course. But it might have to wait until we no longer use touch screen as our primary model to design games. When virtual/augmented reality games become the norm, maybe.