Have you ever used a complex database in a formal, by-the-book, third normal form?

The number of tables explodes, the number of joins become a pain and every single data change requires careful planning.

As for the "many database systems support materialized queries", I only know of a few that truly do: Oracle and DB2.

PostsgreSQL supports them, but you need to handle updating them yourself. SQL server kind of supports them, but are limited.

In other RDBMs you can work around that using triggers (or similar concepts), but that IMHO is definitely a bad practice and the times I've used that (usually because there was no other option) has only brought me grief.