This is a collection of Excel sheets which allow the production of the images seen on pages p71-77 (and your own explorations of you so choose) and in most cases go further in the iteration count.
In all of the Excel spreadsheets you can do your own adjusting of the parameters. The ones there are the ones Wolfram highlights in the book but feel free to play with the numbers etc.
In terms of Mathematica being more powerful than Excel, I'm not sure that is true as Mathematica is a pretty amazng piece of software but certainly Excel is a very flexible tool.