The best explanation for why there is a "Knoppix-style" and "Debian-style" installer is in this post http://www.knoppix.net/forum/viewtopic.php?t=5017

Basically "Knoppix-style" is more in the spirit of the original concept of Knoppix (i.e. no manual hardware setup, no login, easy to remaster) while "Debian-style" is for those who want to use Knoppix as a means to set up a Debian system.