The gravity constant (or the density of the blocks) seems to be a little low. Like playing Jenga on the moon.

You could do that in real life if you did it fast enough. It's basically the same as the classic trick with yanking a tablecloth off of a table.

It's much easier here as it looks like the gravity is quite a bit lower (alternately, the simulation is much slower than realtime) which makes the friction forces substantially weaker.

For an example of the principle in action with a real Jenga game, see: http://woodgears.ca/jenga_pistol/