This isn't necessarily true. If the server sends "Expires" headers, then
the proxy can pretty safely avoid sending if-modified-since requests, for
example.
Even without "Expires" headers, some caching proxies just use simple
algorithms to avoid doing a GET on each request, e.g. only re-requesting
text/* files if they're at least an hour old. This applies not only to
proxies, but also to clients with persistent caches such, if I have a
document still cached on my hard-drive from an access yesterday.
Given these considerations, and the slowly increasing use of "Expires"
headers, State-Info could be expensive indeed.
-- Jim Seidman, Senior Software Engineer Spyglass Inc., 1230 E. Diehl Road, Naperville IL 60563