If Perl doesn't have any modern GUI facilities, this is a major shortcoming in the language!

No it isn't. C doesn't have any modern GUI facilities either, but it's not a major shortcoming in the language. It's not even the biggest shortcoming in the language (that would be the obtuse syntax for specifying pointer data types IMO, followed by the propensity some C programmers have for abusing the pre-processor).

Many (most?) programmers don't need GUIs at all, which is why most languages don't have any support for them. Instead, you use some third party library. Wx is the most common choice these days for portable code, or if you want to target a specific platform then there's Win32::GUI, Gtk for Gnome-ish platforms, and so on.