I did a small amount of maintenance earlier and took the server down while testing. Maybe it cached during that time.
Problem is that so many devices don't check to see if the page is updated and just display whatever was cached last time that IP address was visited.
There is nothing that can be done to force someones device to overlook the cache automatically, I already looked at that before.
It is faintly possible that my post, or Reggie's a moment before, forced something somewhere to recognise the page had changed.
Because things like the content, banners, any clocks or counters one might use are dynamically loaded AFTER the html content (as I'm sure you are aware from sites where you have to wait for ads to load) you can't cheat to make it update.

Another thing - I didn't actually change all the sites over to the new server on one night. I did the slotcardbbs and strikepoint a couple of days before this one and as Bob Baker had managed to post on the new server within a couple of minutes I assumed no-one would need to need to do anything.
I only moved the club and magazine sites at the end of last week (because of the size of the files) and so as some scripts are shared between all sites, devices could still have been caching both old and new IP addresses and of course the old one is dead now.

Tomorrow a.m. my time it will be down for a couple of hours as I need to make one entire backup for the new server after which the daily ones can be incremental. Otherwise as the files increase (particularly the pics in posts) the backup takes longer each day (it was already almost 2 hours on the old box) - this way it should limit it to about 10-15 minutes at 9.30 my time and 10-15 minutes at 10 my time. First one rolls posts into current_archive and reindexes, 2nd one creates the backups. 15 minutes leeway inbetween just in case something is running slow.