A mining full node is a full node that not only holds a block chain, accepts other blocks from others according to its protocol rules, accepts broadcast transactions that come along
but also constructs a new block from its mem pool on top of it according to his own rules, and broadcasts that new block. This is actually the job of mining POOLS. Individual "miners" are most probably hardware owners, that sell their hash rate to mem pools, to mine on the blocks that the mining POOL constructed according to its very own rules.
These nodes are the only "source of block chain". They send out the originals.
EDIT: If people want to be paid for running a full node, there is a coin for that:
DASH.
Every PoS coin is like that. DASH is half PoW, half PoS. Peercoin, for instance, is full PoS. That's the big difference between PoS and PoW: in PoS there's an intimate relationship between user and block chain builder ; in PoW, both notions are totally separated.