Property values often increase from increasing density (ie, replacing my five-million-dollar mansion with a twenty-million-dollar apartment building on the same lot). The zoning doesn't necessarily protect property values as such, so it's an important distinction.

Well, it's code for "keep density low" and "keep traffic out of my property while I go generate traffic on other people's property". The results are the same though.

I didn't say "protecting propety [sic] values", I said "protecting rich neighborhoods". If you'd like more details, I'd recommend reading the book, it is very detailed and well-written.