Quite a few stories of missed flights and nearly missed flights as well as missed cruises on cruisecritic.com - most will bring a tear to your eye. Many are weather related. With that much at risk, it's amazing to me how many people leave for the airport or dock with so little time to spare. It sounds like 4 hours should have been adequate, but now you know that that's only true most of the time. I'm sure some days, it's not enough and if that had been one of those days, you'd be posting an even sadder story. I'm glad it worked out for you. If you had missed it, there were probably ways of recovering, but you'd have been out of pocket some big $$$. Many veteran cruisers arrive at the port with a day or two to spare. They take a longer vacation, explore the embarkation port and are more relaxed as they board. I've seen the opposite (I was guilty once) - the folks that just make the cruise - they are tense and jittery until they drop into their beds the first night.
The cruise I almost missed was my first. We were in Miami by 10:00 am and the cruise left at 5:00. At 3:00, I'm looking for the parking lot/garage at the docks and twice took the wrong road and recrossed the bridge in Miami. they pretty much pulled the gangplank after we boarded. I've flown in 1-3 days beforehand ever since.