http://www.spiegel.de/international/germany/merkel-wins-thir...
A popular referendum leans HEAVILY on one side. 60/40 shows that this issue is very contentious in Greece as well as many Greeks are sick of the poor classes voting in "hand outs" Marxist politicians instead of reforming and fixing corruption, being fiscally responsible, and collecting taxes.
Also, 60 is 50% more than 40.
There have been many extremely close but critical referendums:
https://en.wikipedia.org/wiki/French_Maastricht_Treaty_refer...
https://en.wikipedia.org/wiki/Danish_Maastricht_Treaty_refer...
https://en.wikipedia.org/wiki/Quebec_referendum,_1995
https://en.wikipedia.org/wiki/Quebec_referendum,_1980
https://en.wikipedia.org/wiki/Swedish_European_Union_members...
https://en.wikipedia.org/wiki/Norwegian_European_Union_membe...
60% is decisive, and a clear mandate.