The Arc of Truth

Watching Stargate with the commentary tracks on has led me to consider the nature of plotting narrative over a long serial text. The idea of an "arc" is of particular interest--why such mathematical a term? Should stories really be "plottable"? What would a graph of a series actually look like? What about the financial, production-controlled aspects of a serial narrative?
Given the right information, could a television writer use the desires and narrative conventions of fandom to better control an audience? Do we really want fans writing our canon stories (yes, I'm still angry at Russell T Davies. But Martin Gero, this is for you, too).

Pendulum

This isn't the story he wants to tell
he makes her fall, cloying sweetness gone,
he makes her fly, volition lost in plumbing depths
that plumb three years later, carrying her closer to Xeno's mark

He shapes the world with steep arcs
smooth sines dipping below to break the zero line
he threw her down to this cupped pit to ride the curve
to cushion the rough universe plotted hastily against blue grid squares.