Hi Raghavan,
The brief for this book was to provide a one-stop shop in which all of HTML, HTML5, CSS, CSS3, JavaScript, PHP and MySQL were introduced sufficiently enough to allow readers to create their own apps using them, as the assumption was that readers would have very basic knowledge (if any) of web development or, that if they were already proficient, they wouldn't mind skipping the first few chapters because of all the useful information specific to iOS and Android in the remainder of the book.
There's no getting away from the fact that you need JavaScript to use much of HTML5 (such as the canvas, geolocation and so on), CSS3 for transitions and other effects, and PHP/MySQL (or similar) if you will be using Ajax. Throughout
HTML5 for iOS and Android everything about these web technologies that is different on either iOS or Android is pointed out, so as the reader learns he or she is also taught how to optimize for these devices, and that is the focus of the initial chapters.
Because of needing to cover all the other technologies too I would have preferred a title such as "HTML5, CSS3, JavaScript, PHP & MySQL for iOS and Android", but that was considered too long, and titles such as "Using Web Technologies on iOS and Android" were not considered interesting enough, so the title ended up being focused on HTML5, since there's so much buzz about it right now, and its use implies employing the other technologies with it.
Security and validation is covered in the book, particularly with reference to MySQL and avoiding leaving passwords in plain text, ensuring that salts are used, and dealing with MySQL issues such as attempts at SQL injection. How to properly handle sessions is also covered.
As the object of the book is to allow beginners to go from virtually zero knowledge about web developing, to creating their own apps for the stores, unfortunately there was no room to cover more advanced subjects such as unit testing, because a lot of the book had to be devoted to setting up Xcode and Eclipse, setting up accounts with Apple and Google etc, and then providing ready-made Objective C and
Java wrappers into which HTML5 documents can be dropped for turning into apps.
Hopefully we got the mixture right.