8. Miners don't have anything to do with scalability...they just produce the blocks. The problem is the architecture of a block chain. Mainly the issue is that when blocks get past a certain size (say 1GB for arguments sake) it takes longer than 10 minutes for that block to make its way to all nodes in the network. By then ANOTHER block is produced, which also takes longer than 10 mins, then another, then another. All the nodes just end up collecting blocks and (potentially) reorganizing the chain. At this point it all grinds to an almost halt.
When you say all nodes, do you mean solo miners and pools? Being a solo miner (that doesn't go bankrupt in the first week) in a coin that has enough transactions to require 1GB blocks is a multi-million (or perhaps even multi-billion) dollar business. They can afford faster internet connections. Pools can afford faster connections as well.