Are You saying, that DSCW and it's modules do not have any registry entries? That would certainly be a solution... however that leaves me clueless as to why did the change in the installation process was needed in the first place.
I imagine, that having a copy of the DCSW or it's modules, pirates could make a hack allowing to play offline games for free. Making a Web installer would, probably, make it much more difficult for them to obtain the required files (they still would only need to purchase one copy of each module to hack and distribute them).
Thanks for the suggestion 98abaile!