i use to think wordpress had the worst schema in the world. after actually using it and writing plugins for it, i've come to the conclusion that it is genius. their schema design really makes it very easy for others to "extend" the structure without having to actually alter the schema.
to elaborate on what i mean by extend, wordpress's schema is basically a post table that has the very minimal required columns for creating a post (like the title, date, status and a couple of other), the post_meta table references that post table and basically is used like a huge key/value store. really all it is post_id column (which reference back to the posts table), a key column and a value column. You can add whatever you want to a post by adding them to the post_meta.
this design is copied for all other areas as well, such as users, comments and what have you.
now obviously this kind of design isn't going to work for something like a financial institution where you most likely want a ton of referential integrity built into the schema to prevent accidental data lost and to validate data input, but for a CMS it works very well.
again... it all depends on what the system requirements are.