I personally didn't notice it when I tried it out or read it in the getting started docs. But I probably read it well enough. But I assume few people read the complete manual, when it's not necesary for the setup (in an ideal world they would of course).
As I see it, the fact is that when people use SyncThing to sync items to a folder, and then rely on the synced items (maybe even at some time delete the original), they might risk losing data they need because of this. That's why I have to keep using BitTorrent Sync, even though I would rather use SyncThing if those extended attributes were supported.
I don't know where the 90% number comes from, and how you know that 90% would consider it useless to preserve their files as they are. Also considering the fact that many users of SyncThing are probably advanced users. But I don't want to argue with that, just sharing my thoughts and suggestions. If you can't use it, that's okay. Enjoy your Tuesday.