Its certainly true that a full tank of fuel is the least likely to explode as there is no air, but on the other hand, if a forecourt were well alight the ruptured fuel lines from a full tank would keep the glow going for an awful lot longer. You pays yer money.
Many used car dealers drain fuel tanks, they make lots on it, but when buying its as well to specify a full tank as part of the deal, but then we don't always remember when we are excited about a shiny new/newish car do we. New cars should come full, even if you've paid in the price. Its just bad form isn't it.
AlfaLincs