Gunboat Diplomacy and Full-press Diplomacy are highly-related, but are different games. Some would say that gunboat "takes the diplomacy out of the game", but I think many with experience in this game would disagree with that sentiment.
Gunboat diplomacy is performed via actions on the board, through explicit signals and implied threats, understood in the context of shared objectives (i.e., working against common enemy, uniting to stop a solo) versus competing self-interests.
I think Rokakoma's post (in the first page of the thread that jmo linked) further articulates this better than I could.
Perhaps, rhetorically, one could think of full-press diplomacy as a variant of gunboat that allows for much richer communication channels, but that doesn't mean that no diplomacy happens in a gunboat game.
Anyways, players can flat out lie to your face in a full-press game, so one has to guess their true intentions to anticipate their actions. Cynically viewed, gunboat only removes the lying. Of course, super-tight coordination between allies is also more difficult and players might be a bit more paranoid, but that certainly does not detract from the interest of the game.