The extra 100 manpower they get is to compensate the manpower cost they added to trucks, can't be more clear and precise.
Let you check post 102
100 manpower added at the same time SWS Trucks became constructible. from 240 to 340. 240 was enough to build your first volks squad or kubel right off the bat.
sWS Half-track
One of the first changes that you will notice is that the sWS Supply Half-track is now a buildable unit with a cost associated to it. This change was made to give value to the sWS Halftrack. Players will now have to invest in producing this unit instead receiving it for free which resulted in players driving their truck forward to push infantry. The added benefits of having this unit buildable is the ability to rebuild the sWS Half-track at will in the event it is destroyed. This will make it less punishing to the players who have lost their sWS Half-track.
Tech Tree
Other vehicles have also been reshuffled among the different base buildings. This will allow more flexibility in playstyle while giving a sense of progression and escalation. The cost of tech structures as well as some units have been changed to account for the increase in fuel and munition income.
http://www.companyofheroes.com/blog/2015/11/27/coh2-okw-revamp
Its also the patch that has changed volks cost from 235 to 250, effectively making it impossible to build new volk squad instantly.