Importance of Tools
Applications built with different toolkits are important not just to illustrate the capabilities of the toolkits. Some applications work better than others built with the same toolkit, and so can affect your own development. In particular, different layered tools are available to promote productivity with different toolkits. Glade, for example, is a popular user interface builder that works only with GTK+. Some developers like Glade so much that they specialize exclusively on that one toolkit. While such add-on tools are beyond the scope of this introduction, you'll ultimately need to research how well the toolkits and other tools you want to use work together.
Now you've met the main players in the GUI toolkit game. While you don't have deep experience, you at least know what it's like to code and run your own example GUI application.
Next time you're in a design meeting and someone argues, "We've always used Motif for this," you know enough to ask, "But does Motif give us any advantages that Qt or wxWindows wouldn't do even better?" Perhaps most importantly, you know you can turn to my personal notes on GUI toolkits for references to more detailed information.