Looking at some flights from LHR to MCO in March and the best deals come out with a connection through IAD. However whether this is booked via AC, UA, LH or OS they all offer flights with a connection time of just 1hr 10mins on the inbound

So in this 70 minutes, we are supposed to de-plane, go through Immigration, collect our bags, go through Customs, re-check the bags and then get to the next gate. IIRC, at IAD the international arrivals and domestic gates are some distance apart.

Is this connection even remotely possible to achieve....even if the inbound transatlantic is on time? Why is this connection offered as legal?