The connection fingers at each end would scale with the object using your
approach, and I want constant finger lengths.  To accomplish this a macro is
required:

#macro maSection(len) union {
    box { <-2, 0, -1>, <-1, len-1, 1> }
    cylinder { x*-2, x*-1, 1 }
    box { < 1, 0, -1>, < 2, 1en-1, 1> }
    cylinder { x*2, x*1, 1 }
    box { <-1, 1, -1>, <1, len, 1> }
    cylinder { <-1, len, 0>, <1, len, 0>, 1 }
    texture { pigment { rgb <0.45, 0.49, 0.60> } }
} #end

I also wanted very badly to avoid nesting the objects the way your macro
does.  POV-Ray will eventually complain if you have a lot pieces set up this
way.  What I wanted to do was set up an individual transform for each piece
that would allow them to be placed in a group without the nesting:

// Joint array
#declare maRotArray = array [5] { 23, 29, -10, 15, 30 }
// Joint lengths
#declare maSizeArray = array [6] {10,9,7,5,4,3}
// Transform array
#declare maTrnArray = array [5]

//Connection macro
#macro ManipArm(ob, Lengths, Joints, Moves)
 #local aSiz = dimension_size(Joints,1);
 #local ps = 0;
  #while (ps<aSiz)
  #local rt = ps;
  #declare Moves[ps] = transform {
   #while (rt>=0)
    rotate x*Joints[rt]
    translate y*Lengths[rt]
    #local rt = rt - 1;
   #end
  }
  #local ps = ps + 1;
 #end

 union {
  object { maSection(Lengths[ps]) }
  #while (ps<aSiz)
   #local ps = ps + 1;
   object { maSection(Lengths[ps]) transform { Moves[ps-1] } }
  #end
 }
#end

//Invocation
object {ManipArm(maSection, maSizeArray, maRotArray, maTrnArray)
  rotate y*90
}

You do have a point about working backward from the hand to the shoulder,
though.

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