Being able to produce a GUI app may be more interesting to beginners than crunching some IO with basic console C program. Really, you don't need to understand GObject much to just use GTK+. Surface understanding suffices, and you can structure your program at first in such a way to not need to create custom GObject based classes/interfaces.

Beginners will probably be a bit lost, because the article doesn't go into any depth about event loop, retained mode GUI, GTK signals/handlers, nor does it link to GTK+ docs that would explain each part of the code, etc., etc.