BOM is a abbreviation of Bill Of Materials. BOM basically defines the versions of all the artifacts that should be used in the project - BOM itself doesn't fetch any dependency, it only manages versions of artifacts defined in the dependency part. If you set a BOM in your pom.xml file, then you don't need to specify versions of artifacts that are managed by the BOM.
More information about the dependency management can be found here: Maven – Introduction to the Dependency Mechanism
As for the el expression - it seems that this page hasn't been generated correctly (we will try to regenerate it ASAP) - there should be the last version of arquillian-core which is 1.1.11.Final. Thanks for letting us know