Hi Lee

I've discussed Buran a few times before. The great shame is that the US didn't figure out the same design long before. I think the tunnel vision comes from (a) USAF requirements for Shuttle manuverability - extra tankage could be fitted in the payload bay to reach higher orbits, and (b) a holdover from the original 2-Stage Shuttle which had a lot of propellant tankage in the Orbiter itself, and thus needed its own engines to use it.

But it wasn't an inevitable design choice as the aerospace plane design in the picture from 1965 demonstrates - no big orbiter engines, just little on-orbit/deorbit motors. Numerous aerospace plane designs called for a fully maneuvrable reusable first-stage with an expendable launcher for satellite cargo and to launch a personnel orbiter. Many similar concepts still exist.

Adam