I'll try to find out what's up with the missing posts. I assume it has to do with us having our servers moved.
There are posts removed? I was just assuming and hypotheticising
I wouldn't call it removed, just missing.
Basically it appears that the site was copied to another physical server (based upon John saying a new IP), which copied the database in the state it was in at that time.
People then made more posts (or removed spam posts) on the original server but not on the new server, which then switched off. Now we are on the new server without access to the last posts made on the old server as they weren't copied across.
Either that or something happened to the site such that the database was corrupted, and it got restored to a backup.
I'm disappointed that posts have gone.
As for it happening to other sites, it depends how big they are and how good the host is.
Very large sites like youtube and Google pretty much don't have it happen and when it does they lose very little. That is because they have multiple servers which constantly send data to each other. So if one dies, it would just be no more than the last second or so.
For sites that live on a single server, when it is moved you typically shut the site down so no more database transactions can occur, move it and then turn the site back on. That way no transactions are lost.
But some hosts can be even worse, with no backups at all, so a problem means you lose everything.