Government and regime are not the same thing. Regime is the game and the rulebook, government is just the team roster. America's government changes at every election, but our regime has not changed since 1789. China's government (sort of) changes every five years, but their regime has not changed since 1949. North Korea's government has changed twice (each time by the death of their autarch) in the country's history, but they have had the same regime since China first established them as a puppet government in the '50's.
An Iranian government change (meaning, new people stepping into the same offices) it wouldn't raise our eyebrows. If Iran's regime is changing, that's news.