That smooth, uninterupted approach was due more to lack of trafic in front of you than anything else. We have to do what ever ATC tells us to, speed and altitude wise, when being sequenced into the line up for landing. The autopilot was on, but humans have to tell it what to do, and some are better at it than others.

Now, the last 1000 feet and the touchdown may have been autopilot on, or off. Was it Quatas? They hand fly alot, and they are good at it. If it was Singapore it may have been an autoland, as that's what the Asians do.

In my experience, the 'smoothest' approach/landing is done by humans who have lots of experience, wether they are doing it with the autopilot on, or off, is the question.

The autopilot can be just as rough as any human. It's just a computer. It's still being programmed by a human and constantly being updated with new speed/fix/altitude crossing restrictions. You know the saying; Sh!t in, Sh!t out. So if the programer (pilot) doesn't stay ahead of it, you will get a lot of throttle bursts every time you level off.

Even when the plane is on autopilot, as it is 95% of the time, it's still being 'flown' by a human, who is constantly inputting new info into the FMS (Flight Management System). If he's new to the airplane, he will be a little behind in anticipating what's about to happen next, and getting the FMS set up for the next event.

Just because the autopilot is on, doesn't mean the pilots are asleep! The pilots have to be good at "Running the Box" (FMS) to make it all work out, without a lot of throttle jockying and abrupt level offs going on.

Now, on touchdown, the autopilot is always going to put it down, on target, right where the glideslope intercept is. It will not float, or hold it off just a bit to get a smoother touchdown, as we humans do, but it also won't hold it off just a little too long, and too high, and drop the last 3 feet! That's why if it was exceptionally smooth, or rough, it was most likely a human doing it, not the A/P.

Next time you get a really good (or bad) landing, go ask the pilots if it was an autoland.