* the requests for data themselves are all range requests, which means the content is never cached in Squid/Lusca;
* the responses contain validation information (eg ETags) but the object is -always- returned regardless of whether the validators match or not.
This feels a lot like Google Maps who did the same thing with revalidation. Grr.
I'm not sure why Microsoft (and Google!) did this with their web services. I'll see if I can find someone inside Microsoft who can answer questions about the Windows Update related stuff to see if it is intentional (and document why) or whether it is an oversight which they would be interested in fixing.
In any case, I'm going to fix it for the handful of commercial supported customers which I have here.