LHR hasn't had anything like the amount of snow LGW has. Last night there was over 8 inches on the ground and it was still falling. It's not simply a matter of clearing the runway either - all the taxyways and stands need to be cleared as well before they can think about reopening. It's a massive operation and as fast as they were clearing last night, more snow was falling. Yes, something needs to be done to enable the airport to cope better with snowfall, but I do think most airports would struggle to cope with this amount of snow.
Even if they could clear the runway, the rail network around the airport has all but shut down, few buses are running, and the roads are treacherous, so how would passengers get there? Staff who live locally are finding it difficult and in some cases impossible to get in to work. I've never seen this much snow in the UK in my life - it's way more than we had back in January. Oh and it looks like freezing fog may be on the way as well!