I would guess that that forecase simply stopped before it came down, not that it's never coming down.

Then why is it included in this graph?

Why not? It's a forecast of future production.

Well, it doesn't come down in the graphs' timeframe. Who's forecast is it? And it is really not much of a forecast anyway. This green line runs out of sight in 2010

I think the forecast was just "no peak before 2012." That is a forecast that is of interest, and it doesn't mean Koppelaar thought there would never be a peak.