In a couple of places Salus pretends he's writing a book for the masses — at one point he devotes a couple of pages to explaining the difference between datagram and circuit based networks, for example — but this is not maintained: while Casting the Net doesn't assume a great deal of technical knowledge, it is still very much a technical history, written for those who work with networks and networking protocols. For example, as digressions it contains all the April Fools' Day RFCs: this material can hardly be appreciated by anyone who's never read an RFC or tried to understand a networking protocol.
Whereas A Quarter Century of Unix was built out of quotes, more of Casting the Net is taken up by diagrams, time lines and digressions. Most of these are reprinted from easily accessible sources (like the digressions, many of the quotes are from RFCs), so there is a lot less original material than in the earlier book, and I don't think it is as impressive an achievement. There's still a lot of good material in it, however, and it's a good read (once again, I finished it within a day of receiving my copy). If you are after a compact technical history of the Net then there isn't much competition.