There is an issue using the outer rings of a triple with the extremeties at the back for sure. However, the 2 rings up front are positioned well within the outer extremities of what would have been a triple setup. Therefore, the lateral play is less. Coupled with a slightly thinner chain, it's not so much of a problem. Agreed it hasn't eliminated the basic principles of chain crossover but it has minimised them.
I am running 11 speed Campag on my road bikes, and I can tell you that the 11th cog is not so earth shattering. It doesn't increase your range, but instead reduces the gaps in between gears. Not such a big deal for amateurs, although the Pros love it apparently.
However, the 10th cog offroad is more fundamental. It is just the extra needed to run a double up front and still have a wide and usable range out back without big gaps. So, whilst 11 speed on the road offers only minor advantages over 10 speed, 10 speed offroad is the tipping point to a completely different front setup. So, big difference between the 2.