I hesitate to add to the volume of existing replies, but you could also paraphrase your question as "why do you need to use that fancy loop control when the same thing can be achieved with goto?"

Some new language features are sytactic sugar that aren't really necessary. But like loop control, the our scoping keyword actually allows code that more closely matches a mental model more closely (and safely) than the global-magic of use vars.

I must say I worked on a 60,000 line perl project recently that was restricted to perl 5.005, and living without our really wasn't hard. But it is nicer, and it's not hard to backport if you really have to.