This is related to what we mean we we say 'legacy' systems, do we mean it's simply an old system inexplicably holding out in the modern world, or do we mean that it's a tried and proven stable system that have continued to perfectly fulfil it's use case for 32 years?
I seriously hope he's got a backup strategy for that DOS box.
I get that it's all about familiarity and simplicity (and maybe a little superstition), but I can't help but think that with how complex his books are, something like Scrivener with organizational tools for writers might speed up his process. Then again, I think he likes not being hindered by having to look things up as he goes.