What's the win going from 16 to 12 columns?
You basically can divide it in half (6 columns each), in thirds (four columns each) in fourth (three columns each), in 6th (two columns each and in all 12 plus of course spanning the entirety.
16 gives you only 1, half,
Basically you need look at your design in order to determine what would make most sense.
A very popular choice is to divide it into three equal sizes and then have one of them be the right or left column, while the two others combine to form the other column.
So you end up with two columns one for content and one for navigation (typical blog look)
Grids can obviously also be much more complicated as those used in photoshop, 3dmax, word or windows/osx.
If you want to get really into grids I can recommend probably the best book written about them.
Josef Muller Brockman Grid Systems
http://www.amazon.com/Systems-Graphic-Systeme-Visuele-Gestal...
Was wondering that too. First thing that comes to mind is that 12 columnn is more flexible for responsive layouts, which is another big addition in v2.
For example, since 12 is divisible by 3, it's easier to create a responsive site with 3 vertical sections that collapse into a single vertical section on mobile devices. (Like the Less Framework's mobile layout: http://lessframework.com/. Not the best example, I know I've seen a better one, but can't find it atm, but that gives the general idea.).
Don't know for sure if that's the reason, though.
[edit] Essentially it's more expressive. Another commenter correctly mentioned that it could have the same advantages above for a responsive design. 12-columns allow for greater freedom of expression at all display sizes.
It's a headache, but as I was saying, it's so much quicker to work with than many of the others that I might just dedicate some time to do the work and get on board.
