How frequently is Stack Exchange Data Explorer updated?
Data is updated monthly.
I would imagine that the resources required to run such queries off the live database would be insanely prohibitive, and if it's going to be periodic snapshots a month is as good an interval as any.
Keep in mind that they may actually want to discourage people running expensive queries on their own statistics on a regular basis. I vaguely recall hearing that viewing vote counts has such a high rep requirement largely because they didn't want people hammering the DB server with it.