What is the differece of a XML gui and an HTML gui?
The widgets described in the XML are the difference

I like the possibilities Qt gives me: Powerful widgets, GUI design with a polished graphical tool, internationalization support and many other features I have not used so far, but which are there should my requirements grow.
I just do not believe that web tools have caught up so much that they can play in the same league as desktop tools as far as desktop development is concerned.
The HTML gui is "free"(as in little developer time) the browser already works and it already comes with an scripting language (which is lacking in XML unless you code it yourself afaik).
I highly doubt that the GUI of a desktop application can be written faster in HTML than in Qt, so Qt GUIs are at least as "free" as HTML GUIs. Qt works too, just as the browser, so why mention it? Python is also a scripting language, just as JavaScript, so why mention it?
The scripting language this thread is about has very little to do with coding GUI logic. The Ren'Py scripting language is not equivalent to JavaScript, not by a long shot. It is useful to script dialog-heavy ingame events and was originally developed for visual novels. It is not a full-fledged programming language.
Not sure why you like the XML gui as a resource but you don't like the HTML gui as a resource...
I like both for the fact that you can alter the GUI without altering the code of the application. What I dislike about HTML is that I strongly suspect that its usefulness for desktop GUIs is not up to par with Qt.
You just need 1 folder with 10~20 html files. Perhaps another set of .js and a .css file. No inheritance, no need to search through hierarquies where that thing was defined ... nothing too hard for non-developers.
Technically, I could develop my whole application in a single source file, using only functional programming and builtin classes. No custom classes, no inheritance, only the global namespace and and the local namespaces of the functions. According to your argument that should be really easy to understand, right? Well, it's not. It's easier to see were every variable is defined, sure, but what are they for? Organizing your code in class hierarchies is useful for a lot of reasons and is such a widespread practice that I don't feel I have to explain it.
Placing all source files into the same folder does not make it easier to understand what they do. Again, structure helps to convey meaning.
What kind of GUI modifications are you talking about that you think a non-developer could do with HTML?Nowadays people make some increadibly powerful gui using HTML5 and libraries like YUI and jQuery and all that is available for "free" (again as in little developer time).
Could you point to some good examples of such GUIs, so I can look at them myself?
Oh hell yes. I'm not even going to write any test code until I have the game playable. Third party scripts for individual girls is one of the last things I'll look at. I only mentioned it because it is one area (possibly the only area) where I can see a benefit from embedding Javascript in PyQt. First things first 
I agree with that completely
