Hypothetically that is true, but do any ISPs do these sort of large-scale caching of resources any more? Also, if the site wants to track you that way, couldn'

Hypothetically that is true, but do any ISPs do these sort of large-scale caching of resources any more? Also, if the site wants to track you that way, couldn't they (or anyone in the middle of your connection) just send no-cache headers with everything and a well behaved transparent cache will retrieve from origin every time anyway? In any case, personally I am inclined to trust the operators of the websites I visit more than Comcast, my ISP. I do not want my ISP to do anything to my traffic except to forward it on to the intended recipient.