That's true, but "48 hours to propagate" is misleading because it sounds as though that's business as usual for DNS -- instead of the reality, in which rogue DNS servers cache beyond domains's declared TTL.
Explaining that to clients is hard. We say "it'll take about 72 hours for everything to sync over". If we're switching them to a new IP, we'll leave the old server on until 72-96 hours after we update DNS. We seriously still see traffic on the old server that long after the change, and ~72 hours is about how long it takes to get ~99% updated.
