i think both are a little too late.

nintedo already burned off that market.
though casual market have no loyalty they go for the next thing.
if either sony or microsoft could market their products well, i can see a 3 way war going though
if nintendo chooses to release a budget console again, that console better have something awesome like virtual reality (an example) to compete.

or will be gamecube era all over again.

I think that once these tools(motion controls) are given to the man children(game developers) in and emotionally non harming way(HD) We might see them actually try to incorporate them better as it is no longer an assault on their dreams(graphical realism and immersion) but a compliment to them.

Make a greater impact.... Well Natal is going to struggle, but if Sony make that ball a bit larger, and on the end of a chain, you could have decent wrecking ball, which would be impactful enough for me

I'm almost positive that both the Sony wand and Natal will weigh more than WM+

So I think it's safe to say that a greater impact should occur upon dropping.

Capitalize on the rift created by third parties under utilizing Wii motion controls. There are numerous types of games that would be great on the Wii that just haven't been made. If developers start making original motion games that are of higher quality than most Wii efforts while having no parallel on any other platform, that should give them the foot in the door they need.

WM+ ?

If you really mean WM "+", and not "default" WM then considering WM+ is a ... non event
I say

YES they can !

The install base is too small for either of them to have much of an impact and the only way to increase that is through killer software. Unfortunately who's going to make killer software for an non-existant userbase (in the beginning). I think we are going to see lots of tacked on motion controls (we know how well that worked on the Wii) because many developers aren't going to be willing to build the games from the ground to take advantage of the motion controls..

I see ms having succes, but a good price point of course

Some good points have been made in the previous posts.

Just a couple queries.

What makes some think that more billions spent on advertising and marketing will push natal and x360 into orbit.

x360 ads dominate the UK (from what I have read and seen) and yet x360 is in the wii's wake even with a year and a half's headstart.

Some people see natal and the wand's success as a given. Why?

The way I see it.

If natal is successful wii and sony can easily get their own version of the technology. Sony already has the eye experience and even if an upgrade is required to the current eye this won't be a big deal.

Sony has "copied" the wii motion-controller and we know that the wiimote is successful. MS cannot.

Which is why the OP is misleading?

Natal is "getting rid of the controller". So natal is a controller in the OP's sense but according to MS it is not.

A controller is held in the hand. Natal is aiming to be controller-less. Read the article on the MS website.