Why does active record pattern not work with rich domain models?

I'm reading the architectural patterns chapter of POEAA, and Fowler says that "As the domain logic gets more complicated and you begin moving toward a rich Domain Model (116), the simple approach of an Active Record (160) starts to break down. The one-to-one match of domain classes to tables starts to fail as you factor domain logic into smaller classes. Relational databases don't handle inheritance, so it becomes difficult to use strategies [Gang of Four] and other neat OO patterns. As the domain logic gets feisty, you want to be able to test it without having to talk to the database all the time."

I didn't really understand this. By "one to one match of domain classes to tables", does he mean that only for classes where there is no associations or single table inheritance hierarchy?

And why does factoring domain logic into smaller classes cause the pattern to fail?