Hi Thys,
Justin has those toolbuttons set to disappear when you are editing in places where normal uploads are not supported. Notice that if you click on the Image toolbutton for a comment, you will see the normal Browse repositories is missing from it and you can't upload an image...just provide a link to one.
As for implementing the capability, I can't speak as to what Justin might be able to do, but it seems to me the development would have to be done in the question comment code to allow for uploads there.