This approach offers the flexibility of just building a website that happens to, when accessed using a mobile device, work well as an App. An example is http://forecast.io/ which, if accessed on a mobile device, installs itself as an App on mobile devices without having to access an App Store, but also works well in desktop browsers.
Face it, Internet Exploiter has been holding the web back for years.
The introduction for the book makes a strong case for not only skipping past Internet Exploiter and other archaic browsers, but also to skip past the App Store's and their rigid strict requirements. Mobile web applications can be installed directly on the device, bypassing the App Store, and can be updated more frequently by the application author. Try that on an App Store.
So, what's in the book? Glad you asked.
The first part lays the ground by helping you set up a development environment, and showing you what's new in HTML5. You probably already know HTML, but need to brush up on the best practices in semantic markup for both mobile and desktop, web forms, geolocation, and more. It also touches on media-rich HTML5 elements like SVG, canvas, video, audio, AppCache, database and web workers. The AppCache, local storage, and local SQL storage features let you build an offline disconnected application running in the browser, storing data on the device, while you don't have to manage any user data on your server.
The next segment of the book tells you about CSS3, including color types, shadows, border images, animation, and more. One chapter focuses on responsive web design techniques.
The last segment of the book focuses on the mobile platform, such as touch events, user experience for mobile users, and performance considerations.
The book has you working directly in the actual code and markup, rather than working through a library or framework. They say this is to "ensure that you learn actual code" and to "remove any confusion there may be as to whether a method is native or a framework method." That's not a condemnation of the libraries, however, because the author thinks "open source libraries are some of the best places to find out about browser quirks."
The writing style is very personal and direct, and shows a deep experience with the technology covered in the book.