Look at European map.
Whats are you seeing?
You see that there is an European mainland wich start in Portugal and finish somewhere in the east. Very close to the north is UK, Ireland, and, a bit more far, Iceland, that share (and want to) the main European history.
On the far south-east European's border is Greece, completely out of the European mainland and surrounded either by no-european countries, like Turkey, and by countries that in this decade (at least) dosn't going to join EU.*
It's a matter of basic intelligence, for Greeks, to realise that EU cannot afford, and dosn't want, to lost a country like Portugal (will be easier, more "natural" and acceptable, to replace Portuguese government by an EU "directorate", in case, than lost this real part of EU's territory), but EU can very easily survive - psychological and political as there is no economical concerns - without Greece.
But Greeks just didn't this very simple exercice: look at map and see where they are.
* Let's not talk on Bulgaria (Romenia, Latvia...), the most UE's "failed act".
Note: probably Greece will be rescued by German but Greece going to lost a huge part of its sovereignty. The great true is it will be really good for the Greek people as they going, in some way, to get free of those corrupt and incompetent Greek politicians.