I didn't read the book in question, nor do I know much about HHMMs. Could you summarize the argument? However, I will still try to answer your question. First,

I didn't read the book in question, nor do I know much about HHMMs. Could you summarize the argument? However, I will still try to answer your question. First, note that most of the stuff you read on HN about NNs is about practical applications. Resent research in NNs has lead to good results on hard problems, such as object and speech recognition. Nobody is claiming that these types of neural works are actually a good (low-level) model for how the brain works, they just give empirically good results on some tasks. If you aim is making a model for how the brain works, note that all models are just that: models. Different models can be good at modeling different aspects of how the brain works.