While i agree that the author might go against what he originally claimed he wouldn't try to do, it does not change the fact that a lot of "stereotypes" still hold true for a majority of these cultures. I am german and i have lived abroad for many years. Upon returning, i realized the differences a LOT more than i would have ever been able to before leaving. While it definitely is not 100%, you will find that most germans have a different sense of time and timeLINESS than culturues further south. A classic example is hosting a party: The germans will be the first to arrive (in extreme cases at the exact time of the official start), then the french, then the italians, then the spanish, etc. Of course you can't apply this example to ALL situations.
After all, this is a book about different cultures, not different individuals. You are bound to somewhat generalize groups and place them into categories when writing a book about categories (here, cultures). I don't know what you are looking for here. A disclaimer on each page that all of the above may vary by subject? I don't think this is of much help to anyone.
As with any theoretical subject, take the content with a grain of salt and don't blindly apply into practice across the board. This is merely an indicator to help you prevent common misunderstandings between cultures.
Secondly, you do not have to have been in the country to know or experience a culture (although it greatly helps to further understand it). I am working in a multi-cultural environment for many years. I have had some issues (professional, not personal) due to misunderstandings resulting from cultural ignorance. I was able to recognize SOME (not all) of the communication patterns found in this book within real-life meetings and it was eye-opening.
This is by far not a bible for dealing with different cultures but it is very helpful to sweep away misunderstandings that materialize often once you put two very different cultures in a room.