That's not the way I look at it. GUI is much less about which libraries you have, but more about how quick and easily I can build my user interface with those libraries, and about what tools are available, and how easy it is to use those tools. Today, if someone wants to build a building brick by brick, he still can, but is that a good choice?
"like C and Java offer in the way of GUIs that perl doesn't?"
I said something different with careful consideration. What I said was "java and microsoft products".