The death of technical books (they're not entirely dead -- I still buy some -- but the field is a pale memory of what it used to be) is one of the larger losses to our field.

Those books did things that simply can't be replicated in other forms of media. Being able to drill deep into complicated issues and take the time/space to talk about them with clarity is valuable. Nothing online really does this, and I think it's because the medium doesn't really allow for it.