Everyone also understands when you say 12th August.
Or 8th December, as it were.
Regardless, mathematically speaking, it makes more sense to have the units in a progressive order. Both Japan and the European date system incorporate this (Singapore uses British datekeeping and spelling, BTW), America's system, for whatever reason, does not.
And concerning the ad, oddly enough, that's exactly what someone on GameFAQS suggested. No info, no nothing. Just a big "Wii'. Make 'em curious.
Actually, it's also the ISO standard IIRC, and it's also best because when dates in this format are sorted they end up in ascending/descending date order, which neither the US nor the half-way-sensible-most-of-the-rest-of-the-world systems manage. Three cheers for common sense and the Japanese.
Edit: ISO 8601 defines the standard date format as YYYY-MM-DD.