Jon Tirsen hits the nail right on the head here!
Persistence is only complicated because we make it complicated. Somewhere back in time, it was drilled into our heads that we must use relational databases for persistence. For many applications this makes a lot of sense, but the complications it adds to every day development is just sometimes not worth the effort. Huge advances have been made in the Java world in O/R persistence tools such as JDO and Hibernate (.NET still has some catching up to do here) but using a relational database is just a major headache sometimes.