RE: VC 10 and Il-62
The VC-10 (and Super VC-10) were poor sellers because they were designed too closely to the requirements of one airline – BOAC. The Il-62 sold in large numbers primarily to Aeroflot. Back when the Il-62 was introduced, Aeroflot only flew Russian built aircraft and lots of the aircraft were required because they were needed to replace older types and let us not forget the number of routes the airline flew in the former USSR. To suggest it was a vast network is an understatement. Hence why a considerable number of them were built.
As for the VC-10, it was designed with hot and high routes in mind – Take off performance was very impressive. However, it lacked the range to compete with the likes of the 707 and DC-8, and so only a small number were sold. I still think it ranks along side the 757 and 747 as one of the best looking aircraft ever built.