Correction: the Outer Space Treaty and SALT II banned weapons of mass destruction (nukes, gas, bioweapos etc.), not restricted effect kinetic energy (ie rail gun, Rods From God), directed energy or conventional weapons.
Let's not forget that until 2006-2007 Soyuz crews carried the TP-82 triple-barreled combo weapon in their standard kit. Now they just carry a conventional automatic pistol.
Shoot a metal rod from high enough speed from space and it is a WMD, especially if you drop several of them in the right formation, and/or choose the right type of metal