That's debatable. Apparently that is based on the fact that they have the most toxic snake venom, but I've been led to believe that Hydrophis Belcheri possesses a much more toxic venom, although it rarely bites. And inland taipans are not really aggressive. I think to say a snake is the deadliest it needs to be highly toxic, and have a nasty temperament, so I don't think the taipan can be #1. I'm not sure what it would be, but I think people give the taipan too much credit as the deadliest snake. I mean it can't be the deadliest if the thing rarely bites, right? I believe that all confirmed inland bites have been on herpetologists who were handling the snake.
I would believe the Black Mamba would have to be way up on that list because of it's toxicity, it's higher level of aggression compared to taipans, and the sheer amounts of venom that it is capable of delivering (up to 4x the maximum recorded amount of the inland taipan). A mamba is much more likely to stand it's ground in a confrontation than a taipan, which means a higher chance of a human being bit in an encounter with one.
But that's off topic. I think it would make a decent thread though.