What are DRBD and Gluster if not real-time replicated storage on completely separate physical hosts?

Filesystem corruption without hardware failure is far rarer in my experience. Have you seen an instance that wasn't a proverbial user error?

You never ran reiserfs I see...

Back in ~2004 I watched IT spend a whole day recovering our 60-person startup's main Linux NFS server, due to a software bug in the storage driver. Had to rebuild the whole system from backups.

Yes, I have in fact, in a DRBD configuration. The bug was esoteric, but it happened and was not the result of user error. DRBD and Gluster both allow faults in the VFS layer to propagate to all replicas.

Gluster should by design I think avoid replicating filesystem metadata corruption (but would replicate internal metadata issues in files on top of the filesystem) but DRBD won't... At high volumes I still regularly break Gluster but it'd probably be OK for lower bandwidth/ops use. Not sure what the HN disk usage pattern is though.

IIRC Glusrerfs was the thing that gave me multiple identically-named files in the same directory. Useless.