Well dunno, it doesnt seem quite as worth it for roaches. They still die really fast to marauders and siege tank without any effect from the armor upgrade there, and making a couple of marauders for a terran who already has 2 tech lab raxes isnt that hard.
And even against marines, the extra armor is still not as great of an increase in survivability as for lings. For lings, its 30%, for roaches, its just 20%.

And dunno, I dont see that many players going for early armor. Like speed-carapace-lair with the first bits of gas would be what I consider to be early.
If you are starting armor 2 minutes after the terran got his stim and combat shield upgrades, then it does a pretty terrible job at counteracting them really.