In the Beta a Barb gets 2 Vitality a level. So by level 60 he would have 120 base vitality. Lets say he has +180 vitality on top of that from gear. So Nerves of Steel increases Armor by %100 of Vitality. So I would only get +300 armor at level 60?
Result: +300 armor
The armor of the basic items for a level 60 is about 400-500 for big pieces like pants and legs, and about 200-300 for small pieces like feet and hands. So a lvl 60 would have at least 3000 armor with basic gear.
Tough as Nails increases armor by %25 and Thorns damage by %50. So %25 of my total of 3000 armor would be 750 armor added.
Result: +750 Armor and Thorns dmg +%50
Nerves of steel is just a crap skill. You would have to get your Vitality to 750, just to get the same armor bonus that Tough as Nails gives. Plus Tough as Nails has the +%50 throns dmg.
There are way better defensive passives to pick like Superstition and Relentless. Nerves of Steel is just an extremely weak passive skill and needs to either be completly changed to something new, since we already have a +armor passive. Or they need to at least increase the skill to %200-%250 of Vitality.