It's funny, but for a pipsqueak little country with what, in the great scheme of things, amounts to a small amount of money (Greece's economy is rivaled by Apple Corporation's), Greece actually wields an extraordinary amount of power.
Greece's situation is analagous to that which sometimes occurs in the television show Survivor. One generally unpopular, weak player sometimes finds himself on the outs with BOTH warring tribes. When the two are equally matched, he abruptly becomes the most powerful person in the whole game - not because of his heroic feats or great wisdom, but simply because his vote tips the scale and determines the fate of a large number of other players.
Greece is that unpopular player. It's a little country, but it now has vastly disproportionate influence over the rest of the EU. If it stays in the EU, some short-term stability is gained. If it leave the EU, there's a good chance that the whole house of cards comes tumbling down.
The EU is obviously biased toward keeping Greece happy. If Greek leaders have half a brain, they'll leverage their unique position into getting their entire debt paid off. That will keep ONE domino upright . . . even as it makes the next domino's status more precarious.
The next domino, btw, is likely either Portugal or Italy. They both have vastly larger debt woes than little Greece.