*falls out of chair laughing*
Outlook (and exchange, and most other mail programs) treat mail as data, because storing *thousands upon thousands* of what is ultimately tiny documents (1 per email message!) would have brought most file systems to their knees in short order, regardless of how janky (FAT12!!) or robust (ZFS!) they are.
Ordinarily, I'm in total and complete agreement. I keep reminding my users that Exchange/Outlook Is Not A File Storage System. And yet, I have users with OST files over 5 GB, and PST files approaching the *30 GB* mark, because they can't be arsed to delete ANYTHING EVER.
That having also been said, the ESE database engine that Exchange uses is pretty damned robust and puts up with most of the abuse I (and my users) put it through.