Even if all things were equal, Nintendo portable is still a huge market. While the lines are blurring, I still think DS is a game device, and iOS isn't - specifically with respect to how much people pay/expect from games. The development costs for DS would be higher - as you'd have to build a longer game, but the so too would the margins.
If you meant that Nintendo should be afraid of the massive success of iOS, then yeah, I kind of agree. Still, making a sequel to a monumentally successful mobile game on the most successful gaming console at the moment (or its 3D successor, due to launch soon) would hardly be a bad idea. Yeah, lots of "non-gamers" love Angry Birds, but that's the same market that Nintendo had been going after with the DS in the first place (remember Brain Training?).
I chose to interpret their GDC keynote as an attack from being backed in to a corner. Someone else stole their schtick, and now they are panicking.
I can't help but think that the brand itself has huge potential. Put this in the hands of Disney say, with movies, merchandise and licensing (McD Angry Birds Happy Meals) and the brand is probably worth at least a couple hundred millions. Not saying it's a given, they need to execute properly. Anyone remember Club Penguin (it's still around)...this seems way bigger than that.
This game is also well suited for the ultimate platform: game boy. That could be worth a little goldmine itself.
As for the developer, I have no clue, but I wouldn't bet against their next project.