I've ridden 26" (559) and 29" (622) mountain bike tires enough off road to have a clear idea of what the functional differences are for off road riding. Again, I'm talking about fat, off road tires that are at least 2" wide. Interestingly, the tires in the OP's link are 2.3" wide, which is a very fat tire indeed.

The whole point of 29" mountain bike tires is the abilility to roll over obstacles with less difficulty than with a smaller diameter tire. Just like if you were driving a 4wd truck off road, larger diameter tires will have an affect on how easy you drive over a big rock, for example.

But on a bike, it's not always better to have the bigger wheels; there are advantages, and there are disadvantages. In post #16, I gave real world examples of a couple of obstacles typically seen by mountain bikers, and I gave the reasons I'd rather have one size for one of the obstacles and the other size for the other.

Personally, I think having the choice of 26" or 29" is a good thing for mountain bikers, depending on their riding styles, the trails they ride, etc.; they've got a difference-making option there. But I also think adding another "standard" (584) into the mix is a very cumbersome idea. Just not enough difference, I don't think, to warrant the added headache of another bead seat diameter.

And based on the OP's original link, I don't think any of this has a darned thing to do with 650B tires that are designed for pavement riding-