A number of things affect arrival time, though it is a bit pessimistic to point to padding to make a number look good, rather, it is just smart planning. Flying to Europe from the US, the jet stream can make a big difference, more often than not, planes will get a boost to some degree, but the airlines do not plan on it, to do so will mess up your schedules. I would say that for my flights over the years, most arrived early to some degree.
Another factor for some, since we are coming into Winter, is that airlines plan time for deicing about now. It may be only 20-30 minutes, but it is factored in after "departure time". If deicing is not needed, you can count on your flight being early by that much.