Having used my GT +Premium US model with adaptive cruise control in a fair amount of heavy traffic, I just want to clarify that the US model works just like the Australian model for complete stops that last up to 3 seconds. It's only when you come to a complete stop for more than 3 seconds that you need to use the resume button. (and in most stop and go highway/freeway traffic you'll rarely use resume)
Eg. U.S. model: car in front of you stops => you come to a complete stop => car in front of you starts moving again after less than or equal to: 3 sec. => you start moving again with no driver input, adaptive cruise control remains in effect. Same scenario but the car in front of you starts moving again after 3.01 sec. => driver must press "resume" to re-initiate adaptive cruise control which automatically includes the previous settings (speed).