I don't think Iceland's government defaulted. AFAIK, they simply let their own banks fail and made no move to support them. UK was pretty pissed off because their citizens lost cash in those banks, and they expected Iceland's citizens to cover for them.
Greece is in a completely different pot of hot water. Their incomes (taxes) keep being lower than expenditures, aka salaries, pensions etc. Not getting any more EU help means they will start paying their doctors and firefighters with monopoly money.