My GUESS is that IE provides an interface to allow an application (e.g. QB) to imbed the browser into a window belonging to the application.
There actually seems to be little or no benefit to this (embedding the browser in the application) but that seems to be the way QB does things.
I have a similar complaint about insisting on the use of MS Word to create letters. They could just as easily create the DOC files and let Windows sort out what app to send them to. OpenOffice handles DOC files just fine. QB does it right with excel files -- it simply creates the file and OO is set up to be the default app to handle such files, which it does w/o problem. For some reason QB does it differently for DOC files and won't generate the file if MS Word is not installed.