India & Japan are also heavily dependent on Iranian oil,but it probably won't mean those 2 will stick their heads out for Iran fully.Besides Iran's conventional military forces have not had access to top of the line Russian or Chinese weaponry-the only thing to worry about is their non-conventional(which no one has a concrete idea about) & terrorist infrastructure.
India & Japan don't have a permanent seat on the UN Security Council and the veto that comes with it.