Downloading the whole site is an activity normally done by an ISP, not a work website, who generally do not want to 'webcrawl'.
e.g. if VirginMedia (NTL) has 50 customers who regularly come here, their management systems are clever enough to try and predict that this will happen again, thus they 'cache' your site, to speed up the delivery to their residential customers.
I'd be very interested in how you'll stop this.