Another thing to consider is that Nintendo is consolidating their dev studios, but that doesn't mean that all of those studios are going to be making graphically-intensive 3D games. Neither will many of the indies and smaller 3rd-party devs who are sure to jump on board.
This means that the system will most likely have both types of games, and indeed might get fans of one type to actually be exposed to the other, which I am sure is something they have considered purely from a marketing perspective.
But the bottom line here is that there are, as others above have said, likely to be games that drain the battery much, much less than an Ubisoft game, as their games tend to be fairly (to very) graphically-intensive.
If you think about it, the market for simpler games that are made to be picked up and played for shorter periods on the go might be very attractive, because developers who target that kind of game will be on the same device that dedicated home gamers already own. And vice-versa. Kind of a built-in opportunity for the two markets.