The Earth's not a super computer as far as we can tell. But apparently there is some sort of galactic thoroughfare that needs the Earth to do something. Blowing it up was apparently a misinterpretation of what was really going on.
In the early part of the twenty-first century, astronomers started to find Super-puff planets 
, planets with masses similar to Earth, but radii larger than Neptune's. The existence of these ultra-not-dense planets were a head scratcher until the stars started talking to us.
Apparently one of the oldest Fours in the galaxy came from an icy world, one not easily recreated in other solar systems, and so when they travel around they set up worlds like their home world. A sort of McDonald's highway oasis as they zip around, except its cold so more like a Tim Horton's. The stars told us the Vogons were really Canadian. Supposedly the monarch being on their money led the stars to assume Adams' homeland and the Great North were the same.