I can see pretty much humans reacting the way they did in the book. I wouldnt doubt one minute that whole sections of live humans will be abandoned while the "fittest" hole up in fortresses until the time where they can go out and kill the zombies.
I think the book makes it clear that precisely that tactic is what saves humanity and allows what's left to fight back. The difference being is that those strongholds left behind are regularly resupplied and supported to help them last as long as possible. The rational being that the longer they hold out, the longer they keep the larger swarms distracted.
My favourite bit of human hubris in the book concerns the chapter where some celebrity decided to hold up with a bunch of other celebs and hollywood bigwigs then webcasts themselves surviving in style...I mean you can really imagine some rich idiot thinking this is a good idea. I get the impression the celebs are supposed to be real people, but I've not been able to figure out exactly who everyone is based on the descriptions.