Yes they are depended on for everything… but being integral to the FS makes it nearly impossble to optimise how they are stored or accessed. While having them stored in a database, on the filesystem is obviously quite flexible. I forget who exactly but several of the Haiku developers have talked on this point in the past… on the ML IIRC.
Also acessing attributes and accessing the file contents themselves are often not done at the same time… so performance can be improved by storing them completely separately.
Also dunno if anyone else is seeing this… but the forum is extremely slow the past few days even timing out pretty often.
There might also be a compromise where some data makes sense to put in the xattrs, and some data really makes more sense in a dedicated DB. The problem with how Haiku does it currently is that it gets lost anyway if you move the file to say Linux and open it there… so one way or other the attributes are only portable to BeOS and Haiku themselves.