[DSMan195276]

Entirly true, it's kinda cool to see the evolution - Though it makes sense the games would run bare metal, since that would give the best bang-for-your-buck, and presumably it didn't matter at the time.

The 3DS actually has a somewhat complicated architecture - My understanding is that it has a dual-core CPU, but one core is dedicated to running the OS kernel, and the other is used for games. Thus, there is also a 'kernel-mode' 'user-mode' split in a way, because the core dedicated to running games doesn't have full access to everything, and doesn't have full access to mess with the other core. You can kinda see this in action when you note that the 3DS can only ever have one game running at a time, but certain home-screen applications can be run while a regular game is suspended - Due to the application running off of the OS kernel's core and not the game's core.

This also means that an exploit in a game doesn't automatically result in full-system control - A separate exploit in the kernel is necessary to gain full control over the system. This is completely different from the Wii's setup as you noted - I'm not sure if the Wii had the OS running while games did or not, but regardless since games ran with full privileges a single exploit in a game resulted in full-system control.