If you look at the graph, you see that the bigger the exchange, the bigger the drop in the price in the month after the hack. The last two exchanges on that chart, did not even show a drop in the price after the hack and the price even increased.
I think the amount that was lost, has a bigger influence on the price, because it gets more media attention. <bad publicity>
Some of these hacks was not even just bitcoins, but a mix of Alt coins, but it still had a negative impact on the price.