I have a pair of Hales Revelation III speakers which I love because of the incredibly tight bass they produce. The speaks are sealed. My Watt Puppy's on the other hand are ported and, although they reproduce bass at a reported 20hz, don't have bass that hits you in the chest like the Hales do.
Is it correct to assume then that this is the chief difference between the two enclosure designs, or is this oversimplifying the issue?
Yes this is the main difference when the port is used to extend bass response, as in the majority of designs. In these cases, a ported design will generally have a poorer transient response but will have more energy at lower frequencies (although the roll off will be sharper and there will be more distortion in the LF).
A sealed box is always better in transient reponse