The lip-pout (see the Nonverbal Dictionary) is a near universal sign of sulkiness. In the Netherlands our minister Rita Verdonk was stripped from her responsibility for immigration (a topic on which she is a notorious hawk) after the elections brought about a leftish majority for a general pardon. During the press conference she displayed a nice example of pouting. Although I think it is mixed with lip-compression which is more anger-related. Perhaps she has trouble deciding whether she is angry or disappointed?
Many of the nonverbal cues in the dictionary of David B. Givens are explained in neurological terms, and tied to emotional states. That gives them a halo of uncontrollability and universality. I am not too sure about that. I think we can definitely pout or purse or lips whenever we want to as an intentional display of feelings (that we may or may not actually have). In that case it is a gesture. Whether we can stop our lips from pouting when we are disappointed is another matter, but I would be surprised if we couldn’t. In that sense, not pouting or sulking when we are disappointed can be a gesture as well. If Rita would not pout it would be a gesture of statesmanship. A sign that she can function as a minister, disregarding her personal opinions on matters and carrying out democratic policies. But then again, she may actually wish to display this angry pouting hoping to generate sympathy. Perhaps she is working the crowds for the next elections?