Dysag,
There was another reason that I was told with some force by a BEA pilot - the 737 could carry another four tons of cargo over the 1-11 500 Series - which wasn't helped by the huge amount of Smiths Autopilot in the front of the Forward Freight Bay.
The good looking design heritage continues to fly to this day. The original Canadair Challenger was designed with a large contribution by ex-Vickers BAC 1-11 engineers (even down to the wire numbering system) and that's a direct forebear of the CRJ-1000 100-seater we're testing today.
Check out the distinctly Vickers look here:
http://www.pprune.org/flight-testing...en-flight.html