I think an important factor in irony is that it's an apparent opposition between two aspects of a situation that do not in fact affect each other.

So the diabetic being killed by the insulin truck is ironic, because the contents of the truck no not in fact affect the lethality of being hit by it.

But the death row pardon coming in too late isn't ironic, because the pardon actually could have prevented the death. Whereas your example of 'Speedy' is ironic, because the nickname of the victim has no causal effect on the speed of the pardon.

Examples where the two oposed aspects of the situation actually do affect each other aren't ironic, they're just an ordinary conflict