Newcastle was open as they had very little snow

..... Heathrow has to shift 1000 tons of it. More than 30 per each plane parking bay, and do you know how many they have and how careful it has to be done around a plane? Plus you can't use salt at an airport, the planes would eventually fall apart! One plane had already skidded on the runway, so it was closed for safety reason. You'll find some other countries are pretty much shutdown in the EU, Denmark is at a standstill, a lot of airports in Holland have been closed, you can't clear an airport of snow when it is still falling

..... you don't want to be returning from Manila only to land at heathrow, skid off the runway and die in a fireball

.... on top of that it is dangerous to travel to the airport in such weather, and all safety issues have to be taken into account.