The only thing that the / access gave Klez was (potentially) more files to harvest email addresses from. As far as drive access, the author was much more concerned about having write access to the home directory. If anybody is interested, here is the article:
http://articles.linuxguru.net/view/198
BTW, I do not object to having access to the root drive, but what does a *windows* program really gain from that? Viewing system config files in notepad? ;-> Is it just a solution in search of a problem?
That's the article I read, I don't think there's any reason for having / in the config file, if klez used it, other viruses may use / to infect and spread via linux boxes in the future.