Additionally, a site may receive more orphan blocks than another site which means that they are storing more blocks on disk. They may be measuring this as well which will cause the reported blockchain size to differ from sites that have received different orphan blocks.
Is there a practical reason for orphaned blocks being stored ? Once a block turns out to be orphaned the valid transactions get added to the mempool again.
But what is the actual reason to further store this block if the information it cointains is no longer needed?
Unfortunately, short googling didn't bring a reasonable answer.