When remastering Knoppix or some other CD (I assume any liveCD can be remastered), why do I need to use any special commands or scripting? Why can't I just dump all the files from the CD image onto the HD, crudely tear out all software I don't want or add what I don't have, and then burn a new image onto the disc (or another disc)?

Live distros often use gpg keys to make sure the files are all cosher. You need to alter those as well. Different distros will have other things too. The scripts are designed to simplify the process ... you don't have to use them, but you do have to do what they do anyway.

Take, for example:
http://wiki.linux.net.nz/UbuntuRemastering

Of course - you could always just do what you suggest and see what happens

Just becasue a cd is a live cd does not mean that it was built like all other live cd's. You simply cannot categorize them that way. The Knoppix disc for example is a compressed filesystem that when expanded is much larger than the 700M available on a cdr. SO, you have to compress the filesystem (usually using cloop or squashfs), create a way to boot the compressed filesystem which means also having a kernel available outside of the filesystem. Also lots of consideration is given to the fact that this is a live cd and not an hdd installation so many things like init are modified. A live cd is not just a data cd with a bunch of software on it. There are countless remastering guides available for Knoppix. Some live cd's even have scripts to make it easier.