Of course, schemas change, and it's the migration of live data with those changes that are singularly most likely to break things. Will all your db access code still work? If you're normalizing everything through stored procedures, it gets somewhat harder still.

It's not just testing a single build up... but build ups and migrations from deployed, working options. Some solutions have different versions of an application/database at different clients that will update to "approved" versions in progress. (Especially in govt work)