Actually, fog matters a whole bunch. The worst ever plane crash, between 2 747-200's on the runway at Tenerife was partially due to fog. Also responsible for that crash was poor crew dynamics (in the KLM plane) poor communications from the tower to the KLM plane, fog (the Pan Am plane was on the active runway rolling to the take off position- no taxiways, fog obscured the end of the runway), terrorism (a bomb went off at Palma de Mallorca which closed the runway causing both planes to divert to PMI), fatigue (The PA crew had been flying over 12 hours) and problems in the airport tower.
Do some reading on plane crashes, oftentimes there are several factors. Did you know that the 737 has a bad record with rudder pedal problems? The USAir crash in Pittsburg and a United crash at Colorado Springs were due to rudder problems.....
Waaaay too early to pin a cause on this flight. Just remember, planes crash, and its always a tradgedy, no matter who is on board.
I don't see how they collided on the runway when they disappeared from radar @ +7min.
I don't need more reading.