Microsoft Windows Update and Network Bandwidth?

Brett Glass asks: "As we reviewed the cache statistics for our small ISP today, we noted that the traffic generated by Microsoft's Windows Update feature constituted 45% -- no, that's not a misprint -- of our total throughput. Because so many computers on the Internet run Windows, this massive resource drain occurs whenever Microsoft announces major security holes (as it did this week). The traffic could be greatly reduced, and service to users much improved, if the updates were cacheable at the ISP. But Microsoft has set up the service in such a way that the data can't be cached. (It's digitally signed, so inserting Trojans into the cache is virtually impossible; in any event, no more of an issue than intercepting the data stream.) Are others out there seeing the same pattern? How might Microsoft be convinced to make its updates cacheable, so as not to waste unthinkable amounts of bandwidth?"