Yep, the "moving directory" process is part of what could be done (either the way you described, or from within the shell with "mv"), as well as certain renaming/copying operations, but it is my understanding the it might not be that simple with the iWeb sites that the OP was talking about.
If, for instance, all the links in those pages are not "relative", or use the "borked" path structure, you could "move" the files easily enough and get the index page to display when you browsed to "http://mysite.tld/" or "http://mysite.tld/index.html" and still have broken links from within the .html page (depending upon what iWeb did to them). As I'm sure you niticed, you can have the same issues with FrontP*ge sites.
I agree with your assessment of both NVU and KompoZer - good stuff, IMHO. True they don't come with the "themes", but there are so many good "free" site templates around nowdays, that I think that is less of an issue than it was years ago.