Hi Andrew,

Your belief that Bitcoin has to be constrained by the belief that hardware
will never improve is extremist, but regardless, your concerns are easy to
assuage: there is no requirement that the block chain be stored on hard
disks. As you note yourself the block chain is used for building/auditing
the ledger. Random access to it is not required, if all you care about is
running a full node.

Luckily this makes it a great fit for tape backup. Technology that can
store 185 terabytes *per cartridge* has already been developed:

http://www.itworld.com/article/2693369/sony-develops-tape-tech-that-could-lead-to-185-tb-cartridges.html

As you could certainly share costs of a block chain archive with other
people, the cost would not be a major concern even today. And it's
virtually guaranteed that humanity will not hit a storage technology wall
in 2015.

If your computer is compromised then all bets are off. Validating the chain
on a compromised host is meaningless.