The power glove was not ripe for the market yet. Additionally a glove you have to wear is pretty nerdy and doesn't lend itself to multiple players since it's probably not very comfortable to wear the glove when another person just used it. Also the NES was not capable of 3d and physics simulation...
But not learning that lesson and just targetting a new group seems to have worked for now. Of course there is nothing stopping another company from taking that new audience away and exposing how inept Nintendo is.
Yes there are two things preventing it.
1. Asymmetry of skill: No other company has as much control about both the hardware and software side of a console as Nintendo does, this is critical for the disruption to succeed and a counterattack to work. The software that was released for the Wii was a significant part of the disruption, if this was left to third parties we'd get core games with waggle instead of new market games.
2. Asymmetry of motivation: The other companies don't WANT this market, it's the downmarket, less profitable than the core market. It's the market for crappy nongames for nongamers. Because they think of it the same way you do, Ian, they cannot effectively use the market. The incumbents are happy to leave that less profitable market to the disruptor and focus on their "core competencies". Their problem is that the disruptor slowly moves upmarket, chipping away more and more of the core market until the incumbents are locked into a sinking island.
This is the reason for the E3 2008 "desaster": Nintendo prepared for Sony and MS's attempts to steal their new market away, they focussed entirely on that with announcing the MotionPlus before MS had a chance to speak and focussing on new market games while mostly ignoring the core. The counterattack never came and hence Nintendo's war mode seems kinda silly.
Ian, this IS an established pattern and it IS expected that the core, the upmarket held by the incumbents, looks at the new downmarket with disdain because it looks like a cheap and crappy product for non-consumers to them because the disruptive product is deliberately held lower at the overshot values (which are important only to enthusiasts) while focussing on new values.
Taking the incumbent head-on is suicide since the incumbent has more power at his disposal and can stop the newcomer quickly (MS and Sony have tons of money to throw at advertising and third party moneyhats plus Sony had a massive incumbent inertia with the PS3 that led many devs to make games for them even though the PS3 unveiling was a total desaster and its sales weren't guaranteed), a disruption is effective because the incumbent doesn't realize it's an actual threat until it's too late to deal with it and if the incumbent follows good business practices he will suffer since disruption exploits a weakness in the traditional strategy.