Good Fortune and Misfortune

It does seem strange.

Strange indeed, I've never looked that close at these types of vises before so never really thought about it.

Makes me wonder if the short leg of the L is intended for anything strenuous at all, since heavy clamping force there would put a lot of stress on the joint.

http://www.toolsforworkingwood.com/store/blog/180/The Argument for a Traditional Tail Vise

From the comments:
Code:
Larry Williams

On a traditional tail vise it's not really an "L", it's a frame but part of it is under the bench top.
One side of that rectangular frame is the top of the vise and it provides resistance to racking.
It's actually a pretty rigid and strong structure.

Bit of hints here: http://familywoodworking.org/forums/showthread.php?2945-Tail-vise-or-not-tail-vise
The magazine articles referenced by gary curtis on page #2 would perhaps shed some light or maybe not.. :D

http://www.woodworking.com/ww/Article/Function_of_L_Vises_on_European_Benches_4106.aspx
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Many woodworkers mistake the short "L" of the vise as a convenient
spot for clamping. Please resist the urge, or you'll risk damaging the vise.
The reason for the 90-degree turn is to provide support for a wooden or metal rail that 
guides the vise underneath the benchtop.
 
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