The user should be able to check off which ones they want
The user can. From "Build Options" dialog.

I removed it for 2 reasongs. I couldnt find an easy way to separate windows configuration from linux configuration. And what if you launch the wizard from a Unix system?, then you wont be able to set a windows-gtk-path.
Also my opinion is that, making too much unnecesary pages in wizards, is like polution. I have never changed the Targets names, or paths. And i find the "Build Options" dialog simpler and smarter.
But if it is really needed, someone else could find the way to add the 4 targets. Its not my priority right now.
interesting. it probably does no harm, but do you need so many samples?
Thoose examples are zipped 64kb. This doesnt make harm, but it add a bonus and a starting point for each different project. Like a Glade based project with GtkBuilder or a plugin-based application with GModule starting with the same. A new custom widget which can be drawn with GDK or Cairo. Or using a DrawingArea which is very oft on gtk and can be done in many ways.
With this 64kb of examples, a new user can learn faster how to use a portable toolkit, and take a look before reading a complete tutorial.
It would be nice to have more starting points for wxWidgets and QT and be able to compile them on any platform.
In this way we help a bit more to show people that producing portable software is not hard.
Why would someone deliberately make a software non-portable when no extra code penalty is needed?
Or why shouldnt a portable IDE help to portability?
Cheers.