Election Turnouts

Election Turnouts -- Britt's recent piece about the leverage available in the upcoming presidential election got me thinking. If a 40-45% turnout of potential voting population is a protest against rigged democracy in Iran, what could be said about a fairly well-established democracy that has seen its two flavors of national elections trend from about 63% and 47% in 1960 to 51% and 36% in 2000?