I take the point - but really we're talking hierarchies of risk vs outright it won't work.
Motion control has worked well for the Wii, after all, and there's no reason it won't work for PS3/360 if (and that's the big IF of course) MS and Sony respectively can ensure the controls are purchased by enough of the install base to support motion specific titles.
I'd say right now, until we know how each scheme will launch and with what support its hard to make a call on this crucial point at all.
Also, as ever you can take the opposite view as well and spin things differently - for example while Wii sells the most, etc. it simply doesn't get titles targeted to it that the PS3/360 do - like Assassin's Creed, etc.
With 'optional' motion controls in theory the PS3/360 can play home to non-motion based, big AAA titles like Assassin's Creed, etc plus have motion specific titles too.
In a sense, if they gain enough uptake, these new control schemes will allow PS3/360 to provide titles and experiences targeting the same audience as Wii (potentially positioning themselves as the 'next gen' of such controls) while also targeting the current HD audience which, in a sense, the Wii is locked out from.
But like I say I think the real challenge will be making sure each new control scheme launches with enough titles to ensure a solid install base is secured fairly quickly - once that's in place, so long as money can be made releasing motion control titles for the PS3/360 they will be.
I'd note that on the evidence this far, both MS and Sony are working to make sure they don't launch the controllers with no reason to buy them, and are working on potential titles and with certain developers already.
Of course each scheme may end up nothing more than an off-shot, a perpheral used by only a fraction of the install base - something Nintendo sought to avoid by making the Wii 'all or nothing' by making the motion control central to the console and effectively 'mandatory'.
Either way it's sure going to be interesting to see how this develops.
Try to be reasonable... its easier than you think...
