It would do better sales wise, lets face it people don't buy I-Pads as game devices at least usually they don't. They buy an I-Pad to watch movies and listen to music to surf the web and enjoy tons of informative apps. A 3D I-Pad would be a nerds wet dream and millions would rush out to buy one. Even if 3DS had the movie playing capabilities of I-Pad and the music store to match the screen is still much smaller and the device caters to gamers a much smaller market then I-Pad.
So sales wise yah I-Pad would own 3DS. By how much? I'm not sure but they would definitly take Nintendo out sales wise.
But what about game quality? As gamers we care about the games not the movies and the music. With no Apple first party content and even if their was Apple lacks the game studios or capabilities to make Microsoft level games let alone Nintendo. The third party games on I-Pad 3D would be terrible. The majority of the developers would take their existing 2D I-Pad 2 games and port them to 3D. A few brave developers would make new 3D games but they would be crap in comparison to any of the three first parties or even half the third parties.
Even the games from third parties wouldn't be up to the task of taking on their better offerings on 3DS. Personally I think Apple should aquire Gameloft and make them Apple first party, they would likely be one of the highest quality 3D developers.
In the end sales wise I-Pad 3D would dominate, quality wise Nintendo 3DS would still own. P.S I fully expect 3D I-Pad either with I-Pad 3 this year or in the next 2-3 years. They will go 3D pretty soon.
-JC7
"In God We Trust - In Games We Play " - Joel Reimer







