Why is it that GM and Ford can design a driveshaft that doesn't need to be rebalanced during its lifetime?

I don't understand the design at all, but I find it peculiar.

German Over Engineering at it's finest....

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Bryan Harter
1992 500E Smoke Silver
2002 CLK55 AMG Cab Silver/Black
2001 Harley Fatboy - Pearl White
2004 F150 FX4 Silver/Grey
1969 GTO Liberty Blue
1956 F100 Black