>What's really annoying is that the code's probably quite pretty and well
>organised, unlike this big bowl of widget soup.

The code is the interface. And there is probably not much of it!
This is just a GUI front-end for wget.

And not much effort was put, to hide the complexity of wget.

This is not that that complicated to call for dedicated designer. The guy was just lazy!

Maybe a GUI that maps a CLI isn't such a good idea. Maybe the program should have been writen from the start to support a GUI, or that more code around the CLI should have been writen to make it more interactive and not batch-like