Bicycle Mechanics - what good does alternative cable routing do?

http://sheldonbrown.com/dura-ace.html

So, Sheldon, (or anyone who knows realy) explain how bending a cable up through the pinch bolt instead of going right through changes anything about compatibility.

It alters the derailleur's pull ratio.

By moving the point where the cable is anchored, you change the distance the derailleur moves when you pull the cable a certain amount. In other words, when you move the shifter one click, the different anchoring point causes the cable pull to have a slightly different affect; in the case of alternate cable routing, it causes the derailleur to move slightly further with each click of the shifter-

Let me say it another way:

If you anchor the shift cable closer to the pivot the same amount of cable pull will move the derailleur farther. It doesn't take very much to make a difference.

The old DA shifters pulled less cable/shift, so this routing pulls enough cable for you to be able to use the other model RDs w/early DA shifters.

Too bad it's not the other way around. Plenty of old DA RDs around, just not enough 7&8s DA shifters

Plenty of old DA RDs around, just not enough 7&8s DA shifters

Use a 9-speed shifter with your 8-speed DA derailleur. Spacing of all Shimano 9-speed rear shifters (DA, Ultegra, 105, mountain...) is identical to the spacing of 8-speed DA shifters and derailleurs.

Use a 9-speed shifter with your 8-speed DA derailleur. Spacing of all Shimano 9-speed rear shifters (DA, Ultegra, 105, mountain...) is identical to the spacing of 8-speed DA shifters and derailleurs.
I know, just not quite correct when you're anal on a resto