Is it really the RTOs responsibility to deliver PD sessions throughout the year for their trainers and encourage subscriptions to websites and newsletters?
Well the answer again, as per normal, not black nor white. 
It can be, if it is written into the policies and procedures….
or ….
it could be the Trainers / Assessors responsibility.
It totally depend on what you have decided within your RTO and written into the RTO systems.
If your model is to have the Trainer and Assessor ensure they are meeting the requirements, then you will need make your RTO system clear so they spell out the requirements of each trainer. Hold them accountable for documenting their PD and work experience or liaison with industry.
An excellent model is to recruit part-time or contractor trainers, who actually hold down a position with the industry they are training in.