The way I had it explained to me by a first aide instructor, although gram for gram of venom, Australian snakes are some of the worst, the delivery system is not as efficient.

Venomous Australian snakes generally have a groove down the outside of the tooth which the venom runs down. So when bitten a lot of venom will get soaked into the clothing, and it generally goes into the lymph node system more than into the bloodstream.

Whereas Indian snakes have a hollow tooth like a hypodermic needle which delivers the venom efficiently into the bloodstream.