Who knows, lol. The only way you'd want to buy a more expensive 24-70mm IS over the 24-105mm IS is (wow, IS is, what a mess that is!) if the 24-70 were much much better optically.
My guess is that Canon added the pseudo-macro mode to the new 24-70mm to try to justify a price increase. The new 24-70mm also has 3 less lens elements than the 24-105mm, so it's probably a bit cheaper to make!
I bet that they did 24-70mm f4 IS instead of an update 24-105mm IS, because it'll cut into 24-70mm 2.8 sales less. I bet...maybe not, but hmmm...
Also, $850 for a 35mm f/2 is insane. The profit margin in that must be sick. You'd think it'd be like $500 or so maybe, max!
If the 24-70mm is really like $1500+, and really is going to be the 6d kit lens, Canon's 6d will get DESTROYED in sales by the D600. Think about it... 3500 or so for a 6d+24-70mm kit, vs 2500 or so for the d600 + 24-85mm kit. Even if the 24-70mm is much sharper, $1000 more is crazy. Nikon's 24-85mm VR is overpriced, imho, at $600. $1800 for the Canon competitor would just be insane, that's three times the price.