That does seem to be the obvious conclusion, yeah. Like I said, I think to make the tier work it wouldn't even need to be a creative talent though... even a straight out passive damage reduction like hunter's iron hawk, or something practically the same with a little flavour (10% damage reduction while SnD is up? 15% reduction of damage over time effects on the Rogue? Plenty of simple talents). It wouldn't be spectacular but it'd work, and the talent tier would actually have a bit more meaningful choice.
As far as other non-lethal poisons go... yeah, think they are just being a bit lazy or scared to make changes because they don't want to rebalance anything.