One word about the general graph.
In dec 2010, only norht marauders were sold according to my table. So the graph is very high for this date, and we have to weight well the value of this month.
In May 2011, the same.
In August 2011, 11 sells of OOP stuff, but 3 Dragon Pricnes and one Hammerers, so here too prices are particularily high, but it's a statistic anomaly we have to weight.
In September of this year, as said, i did not entered recent sells, so the graph goes down. But it does not reflect reality.