The armor system in TA works with damage reduction in % instead of absolute values. That means, 40 armor upgrades aren't a problem at all. Because the higher the armor upgrade, the lower the actual armor gain. You can calculate the effect by using this formula:
Damage Reduction (%) = 1 - 0,96^Armor Value
With 10 Armor you would have 1 - 0,96^10 = approx. 33% Armor Reduction.
With 40 Armor you would have 1 - 0,96^40 = approx. 80% Armor Reduction.
So even if someone got all armor upgrades, a "0" attack Marine for example would do 20% damage to the max. armor upgraded unit, meaning 1 damage out of 5 in total (e.g.).
The hero upgrades will be present in patch 15.