Does maven automatically download artifact dependencies?

To answer your question, no you do not need to include all of the dependencies listed in the artifact dependencies section. It is my understanding that when you include a dependency in your pom file, maven will automatically download any needed jars. I am inferring this due to the fact that I personally don't add any of the artifact's dependencies other than what I need to my pom.

For example if I wanted spring-core I would do the following:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>3.2.8.RELEASE</version>
</dependency>

And maven will automatically take care of the dependencies for me.

A good way to test this out is to open a new maven project in eclipse and specify a dependency such as this, update the project, and then check in the Maven dependencies folder.

For fun, I experimented with this and it is indeed true, Maven will download any necessary dependencies when you update your project. After putting only the above dependency in my pom.xml file I got the following: