You are correct that a 51% attack depends on hashing. Other attacks, Sybil, etc. depend on gaining network access to the (a) real bitcoin node with the latest b

You are correct that a 51% attack depends on hashing. Other attacks, Sybil, etc. depend on gaining network access to the (a) real bitcoin node with the latest blocks -- more nodes, I guess, helps prevent people from being unable to find the true network. Hence jgarzik's push to put bitcoin nodes into space to beam the latest blocks to earth, à la GPS.