And my perception would be that the TV experience would be squinty at best, although I've not tried it.
My phone has a 4.3" screen, which isn't much smaller than the screens on planes. The latest generation of Samsung and HTC phones have even bigger screens with 720p displays. Maybe I'm just used to squinting at small screens because I've been playing handheld games since the Gameboy, but modern phones are perfectly fine for casual viewing.
Meanwhile, games on the iPad are $1.99 or $2.99 each, and there's billions of good ones that play much better than a DS ever could.
Can't argue with the cost argument, but I'd dispute the quality. I've got a ton of great games on my iPod, but very few stack up against, say, Ocarina of Time on my 3DS, or Dragon Quest IX on the DS. And, regardless of production values, for some types of game, touch screen controls are no substitute for physical controls.