I'm with you on that one, The people that matter and the people with the cheque books wouldn't care less if it was an A380-800 or an A3XX-100 but the reasons I gave for them choosing it are correct.
To quote from an A380 book I've got,
But why A380, rather than A350 or A360, both of which had been th enext logical designations in the Airbus numbering system? Although the user of the numerical 8 was already believed to be good luck to many asian cultures, and therefore a consideration toward the large customer base of the region, Forgeard said the final designation was selected because "8 suggests double-decks, one on top of the other".
...
Then there was the question of using the higher end -700/-800/-900 designations for the derivatives straight out of the box. Airbus Chief Commercial officer John Leahy said that this approach was taken because the three versions were fully developed aircraft and the -100/-200-/300 designations would be subject to earlier obsolescence and therefore lower residual values.