[simonh]

File systems are databases in a small way. They use b-trees and such, but they don't enforce a rigorous global type system, don't enforce a table structure because everything has to have a schema, don't have the overhead of a query language to interpret every file access command, didn't ensure that all file accesses be ACID compliant, etc.

WinFS imposed all of those things and the associated overheads and much, much more every time you accessed anything.