ok, the following is an explanation for the moves and stats:
Rash Nature: sandstream already boosts its special defense by 50%. if you consider that Rash will only reduce its special defense by approximately 10%, then its base 100 sp def is, in a way, increased by 40%, which would make it a 140 base sp def stat. that's more than enough. also, if you consider sandstream, it takes away leftovers recovery, so bulky waters are still less of a threat.
also, -Spd Natures make Tyranitar slower than Blissey and would require speed evs anyway, which would take away from the Attack evs put in for Crunch.
why Crunch? Focus Punch will reduce Blissey's HP low enough to KO it with Crunch next turn instead of having to give it max HP evs and IVs so that you have to set up ANOTHER sub and use Focus Punch again. also, Crunch + Flamethrower covers everything EXCEPT Heatran, who isn't much of a threat anyway. Crunch is also preferred because it has a great tendency to severely hurt pokes that have a capability to cripple TTar -- Dusknoir, Cresselia, Gengar, etc. it is also awesome for pokes like Gallade who resist fighting attacks but has a low defense stat. then you have pokes like Slowbro who has a good defensive stat, but has no means of boosting their defense unlike their sp def and atk stats (Calm Mind).
why Flamethrower instead of thunderbolt? Heracross. that simple. Focus Punch and Dark Pulse are NE on Heracross, and with 95 base sp def, Thunderbolt is a 3HKO to Hera. if you consider the circumstances, Close Combat is a OHKO to TTar. better to near OHKO Hera with Flamethrower while behind a sub, and then let it die from Sandstream that same turn. also, if you consider Close Combat's reduction of defenses, Flamethrower + Expert Belt should OHKO it.
also, Flamethrower makes TTar more of a threatening factor to steel types in general who would feel the need to come in before -- Scizor, Forretress, Bronzong, Metagross, etc.
i think this ttar is pretty much flawless and i wish i was using it myself.