Rogers itself once explained this in its FAQ. That FAQ has since disappeared, but it was quoted in full on the site of the Residential Broadbant Users Association (here; an archived version from Sept. 2003 can be seen here).
The Rogers FAQ defines a proxy and describes how it is used:
The proxy is a local HTTP (web) server internal to a regional/main data center, which caches (stores) frequently requested content. It was originally implemented in order to greatly reduce unnecessary network traffic, particularly backbone traffic leading to the @Home Network in the US. When you want to access a website via your proxy, you send a request to your proxy, which then checks to see if any of the related content is stored locally. If it isn't, the proxy will access the remote server and send back the information you originally requested. The new information is then cached on the proxy for a predetermined period of time.Note that the Rogers FAQ actually tells us that accessing a site through a proxy will send the proxy to the site. Any logs at the site will capture the proxy's IP. This is presumably why so much traffic can be identified for these years (see here and here and here) -- because 66.185.84.204 is forwarding numerous users. Also note that its job is to act as a web cache — indeed, as I conclude here, this is what the "wc" in wc09.mtnk.rnc.net.cable.rogers.com stands for.
