Not quite true - Greek bonds did not have significantly higher interest rates than other Euro denominated bonds.

Greek bond chart: http://www.bloomberg.com/quote/GGGB1YR:IND/chart German bond chart: http://www.bloomberg.com/quote/GDBR1:IND/chart

Go back out 3 years, and you'll see that as late as December 2009, the yield spread was minor, and that it didn't start to really diverge until July of this year.