I don't have this book, book working from the download code, I made the following changes to get the behavior you want. If your project is working currently, duplicate it, so that you have a backup.
The following changes are to the RootViewController.h RootViewController.m and RootViewController.xib files.
As written the RootViewController is a subclass of UIViewController. Make it a subclass of UITableViewController. Delete the UITableView *taskTableView instance variable and property in the header, and remove the @synthesize for this ivar as well. In the .m file remove self.taskTableView = nil; from the -viewDidUnload method and [taskTableView release]; from the -dealloc method. Change all other references to taskTableView in the RootViewController.m file to self.tableView.
In the RootViewController.xib file delete the outlet from File's Owner to taskTableView (it should have a yellow warning sign, since the ivar no longer exists) Connect the File's Owner view outlet to Table View.