I think the point is that the rules have changed to simplify how war machines are taken out, but in doing so GW have over-looked the Poisoned Weapons effect.
Under 7th a typical war machine consisted of the machine (T7, W3) plus the crew (T3, W3 (assuming a typical 3 man crew)). To take the warmachine out through shooting you had to either kill all the crew or kill the machine. If your shootings were Str3 then only 1/3rd of those hot the crew. Of those only 1/2 wounded. So you would need to inflict 18 hits on the machine to take it out. And that was the easy way - 18 hits on the machine would yield 12 hits allocated to the machine itself - assuming you could wound on a 6+ that would not destroy the machine.
In 8th the whole thing - crew plus machine - are reduced to an aggregate 3 wounds. To compensate, you have to wound against the machine's T. If you are dealing with ordinary (non-Poisoned ) shooting, it turns out you still need 18 hits to take down the machine and its crew.
What GW has forgotten is that increasing the T of the target being shot at may compensate for halving its wounds with ordinary shooting but it has very little effect if the shooting is with Poisoned Weapons. The consequence is that certain armies (Lizzies and Skaven come to mind) have received a huge (and undoubtedly unintentional) buff to the effectiveness of their skirmishers, whilst armies which rely on war machines (Dwarf, Empire) get a kick in the nuts.
What's particularly frustrating is that the boneheads at GW could have achieved their aim (simplifying shooting at a war machine) without creating this shift in game balance for certain armies. All they had to do was reduce the aggregate wounds to the number of the crew, say shooting attacks were to be resolved against the crew's T and armour, then give the crew a 4+ ward save because they can hide behind the machine.