I doubt every vampire in the world is attending the vamp-fest in San Fran, though. One: There is no way to manage such a gathering, since Xarus is not a true Lord of Vampires (as Dracula was...See my above post). Xarus in no way, shape or form is able to control the entire world's population of undead.
Two: Nine thousand, may indeed be a good population number for vampires world-wide, but keep in mind...Not all vampires create new vampires with every feeding. Many vampires take only as much blood as they need (which doesn't always kill the victim), while others ensure the victim will not come back as one of the undead by killing the victim first or during feeding (by neck-snapping, decapitation, etc...). I can't imagine the world's population of vampires would range in the millions either, especially after events such as their recent battle in Captain Britain and the past event of the reading of the Montesi formula by Dr Strange (which destroyed every vampire on the planet). Also, you have to take into account the armies of vampire-hunters that exist in almost every country in the world (including Blade, who's probably killed thousands of vampires in his lifetime).
I feel the number is necessarily inflated for dramatic purposes (and not done very well)...One thousand vampires or even eight hundred would be sufficiently menacing.
Dana