The brilliance of Cadbury's approach lies in what it leaves out. Imagine, at the end of the ad, if the gorilla had paused to enjoy some chocolate; suppose a cheesy voice-over had forcibly supplied the logic with "there's almost nothing that can beat the joy of Cadbury's milk chocolate". You then would have been left with a pretty average, if still watchable, ad.
Like a few other landmarks - such as B&H, First Direct or the "lucky star" advert for Mercedes - it works because it does not hand-hold the viewer down every step of the logical path.
The convention of TV ads holds that anyone must be able to parrot a one-sentence explanation of its single and unambiguous meaning.
But what is to explain the millions successfully spent on non-explicit forms of communication? No-one feels that an elegantly redesigned new pack or an Olympic sponsorship needs a sentence of justification.Why do we apply certain standards in one medium which we believe don't matter in another?
And where is the justification for this framework which has become the standard strait-jacket approach to TV?