I personally don't blame George V for what happened to the family. He was bound by his government and honestly, I can see why the government acted this way - between protecting the status quo in their country from what they thought as dangerous and helping the King's relative,s they chose the first. And besides, although they had nothing in common with the Bolsheviks, I doubt that they held in high regard the political system of tsarist Russia. A constitutional King can only do as much in the end of the day.
VM, the situation with the Greek royal was fundamentally different. The military movement that took over after September 1922 had nothing to do with the Bolsheviks' ideology, methods or goals and had everything to do with the National Schism. They certainly had no wish to harm Philip, his mother and sisters they way Alexandra and OTMAA were by the revolutionaries - their worst possible fate was exile and poverty, not death. Again I have to stress that I doubt that George V had much influence on the matter, because it was once again a matter of politics decided by the British Government. The British government fought to save Andrew's life, sure - but it fought just as hard to save the other 6 people who were facing the same charges and the same penalty , even though they didn't succeed. It was politicians who pulled the strings once again. So I really fail to see how George V had more to do with saving Andrew from his fate than leaving the Romanovs on their own. To me he seem to deserve the same credit on both cases