Handheld revisions were necessary due to the nature of the hardware, Nintendo doesn't have to release a whole new system just to reach new gamers like they do handheld devices. Many here are forgetting that Nintendo already revised the Wii, or should I say the user interface, to attract new customers.
Nintendo noticed that the Wii remote alone wasn't enough, and thanks to values changing to user interface they didn't need to release a revision of the Wii hardware, they just needed to add 1:1 capabilities to the Wii remote. So I stil do not see how the benefits of going 'HD' outweighs all the negatives (increased cost in development, splitting the userbase, confusing consumers).