A lot of airlines flew that route, for example 57 Lufthansa, 75 Singapore Airlines and 5 United Airlines flights passed over the area the last week before MH17. malaysian airlines where just one among the others. just bad luck for them it where that flight that where hit. A 777 from singapore Airlines where around 90 seconds behind when they got hit.
It is pretty easy to see where the missile came from, both sides has the capabillity to do that and it seems pretty clear that they where shot down by misstake by the rebels. Guess the lesson is that providing advanced weapons to the enemy of the enemy is a risky buissness the could bite u in the rear parts.