A good top-loading NES, I believe you mean. Unless you've been doing the occasional pin-surgery.
I don't think it's so much a matter of simplicity as it is control. If you depend on them directly for replacements, and the stability of your library, then you're less likely to do anything out of warranty and/or anything that their repair guys will deliberately penalize you for (a practice already well-established with the Wii). Read: It's one more method to make sure you use their products their way.
I think it is of simplicity as well. The whole Nintendo product range reeks of simplicity. The Wii, for example, astounds me as to the complete and total lack of customization options it has, the way they never really updated the channel system or used extra memory for anything useful other than VC game storage, the way so many features and channels they add are completely reduntant and infantile, and how there's really a TON of easy-added options they could make millions with, that they just choose not to add.
I know it doesn't appeal to us particularly, but imagine the Wii with Facebook and Twitter channels, like the 360 has. No matter how incredibly basic they'd be, they would have a LARGE success. And I know Nintendo wants to stay as far away as possible from the app market and keep people in the dark ages about how all games must cost 40 bucks or more all the time, but with how widespread their software is, they could make so much from that market. So much more they're making now.
I know Nintendo isn't one to shy away from money. Why are they doing so now?