The Vogons are beside the point. they are simply slug-brained bureaucrats. Ultimately, they were merely pawns, manipulated by a shadowy cabal of psychiatrists, who wanted the Earth eliminated in all possible parallel dimensions because they wanted all possible Questions to the answer of Life the Universe, and Everything completely eliminated forever. (since they'd subsequently be out of a job -- it's a concern as old as Deep Thought itself)
The following paragraph is offered for the confused (who may rest assured that it is unlikely to alter said state).
It is of course well known that the Ultimate Answer to Life, the Universe, and Everything is "42". Unfortunately, Arthur Dent's brainwave patterns are the closest the Universe ever gets to figuring out what the Question actually is. He was present on the Earth (which was, in fact, a computer built for the specific purpose of sussing out the Question, running a multi-million year program so complex that lifeforms living upon it formed part of its operational matrix), moments before its program was about to reach completion and spit out the Ultimate Question (and indeed moments before it was blown to smithereens by the Vogons ostensibly to make way for a Hyperspace Bypass). As a result, imprinted upon Arthur's subconscious is the final result of the Earth's program: "what do you get if you multiply six by nine?" This is no doubt some kind of perversion of the real Question, due to the fact that a few million years prior, the pre-human natives of Earth were wiped out by the useless castoffs of another civilization, which had cruelly shipped off all their moronic middle-men, telephone cleaners, and advertising agents to exile on Earth. Arthur Dent and every other human on Earth ended up descended from these idiots instead of the Neanderthals that had evolved on Earth as part of its program, and as a result its program had become corrupt.
Even in its corrupted form, Arthur's answer hints that the true Question may indeed be just as inane as the Answer. At the risk of editorializing, this supposition seems in no way inconsistent with my personal experiences within the Universe in question.