As someone who lives in an earthquake zone I think this theory isn't consensus by any means (that earthquakes release tension and reduce the probability of a followup earthquake). That is no one actually knows if having a strong or a weak earthquake increases or decreases the probability of having another one. Once we can dissect the earth and model accurately what's going on in there it will become physics, until then it's more like geology... Tsunamis can also be triggered by earthquakes in different locations.

I'll agree with the part that earthquakes aren't independent events...

EDIT: "The opposite occurred in Turkey along the great North Anatolian fault. A large quake in 1939 sent stresses farther down the fault, triggering a 60-year series of quakes whose latest installment was the deadly Izmit earthquake of 1999. The stresses have risen in the crust near the city of Istanbul, and a quake there is now considered more likely. " - http://geology.about.com/library/weekly/aa022303a.htm