Having fully swept tail surfaces as per the Ilyushin 28 also moves the effective centre of the surfaces rearwards without extending the fuselage. With the presumably quite heavy tail gunner's compartment there, extending the whole fuselage back could have caused centre of gravity issues.
As for general aviation aircraft (IAI Westwind, Piper Aerostar), I'll go with the 'looks fast' theory.
Last edited by Mechta; 19th Jul 2012 at 18:09.