The Iterator pattern he describes can become much more powerful if there's a way to say "do this on all items in a collection where each item is independent". This enables parallel processing.

In his example, a simple sum of item values may be even more optimizable by using a Divide-And-Conquer approach, Map/Reduce, etc.

Depending on your system's setup, you can get significant speed increases by using these approaches because they work well on multi-processors and multi-cores.