Well, scope localization was not really the main issue, but a nice side benefit. The key point to our is that it is a single syntactic declaration for a single name, and as such, a location on which you can hang various extra modifiers controlling your view of that variable. That was envisioned from the start, though we're only just now getting there with Perl 5 "attributes" and Perl 6 "traits". In essence, the our declaration functions as a peg on which you can hang other declarations, which use vars could never do.