I can't speak for history, but the reason I did so was availible materials. The
crossmembers of the base were only 52" long, so the base was going to be
narrower than the top. 
I spent many hours sitting on my sawhorse staring at the top sitting on the
base deciding what relationship the top and base should have. I decided on this
to keep the arm part of the shoulder vise fairly small and give myself room to
store my sawhorse under the end-vise side of the bench.
On the other hand, I haven't had any problems with it. I can sit on the tail
vise (I've never been mistaken for an Olympic runner) side of the bench and it
doesn't tip. I also can pound on that end with no ill effects.

Maybe that does speak to history. I like the space on that side to pull up a
sawhorse and draw out plans or chisel. Maybe historically the space was to
allow someone to work in a sitting position and still have the bench in front
of them. Maybe there was some resource or building method that limited the
sizes of bases, too. 

Of course, all of that is based off of personal experience and no direct
reference to anything concrete from a historical perspective. 

-Clif in Dallas, TX
(pumped Jason is daydreaming of my bench)

--- Joe West  wrote:
> All
> 
> Why is the tail vise end of a traditional cabinetmakers workbench, like 
> Clifs, unsupported?  That end of the bench hangs way over from the legs.
> 
> Joe West

=====
I saw the angel in the marble and carved until I set it free.
      -Michelangelo

	
		
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