The are copying content wholesale to keep the traffic from getting there.
Though they are supposed to do a cache refresh every time someone hits it.
With reports of BING DOSing site scrubbing for content (and specifically using robots.txt as a guide of *where* to go), I seriously doubt they are playing by the (implied or otherwise) rules.
Per nostra Pentium Quatro cum 2 gigahertzum e bus de cuatrocentum megahertzum... Deo Gratie... Per nostros Quinientum Doce megabaitum de RAMus... Deo Gratie... Per nostra GeForsum Duo Mu Omega cum centum ventiocho megabytum de memoria Delta Delta Rho... Deo Gratie... E por nostro casum de aluminum con sweetum modus e infinitum blinkenlightenus... Amen
93 ms