This is because TestNG doesn't guarantee that this method is called right after the method it depends on. This could lead for example to following scenario:

1. call method which I depend on
2. restart server (Arquillian incontainer mode restarts server after 250 tests)
3. call method with dependsOnMethod param

The deployment in this case should survive the server restart but it's not guaranteed anyway as this currently manifests with following problem on Solaris architecture https://issues.jboss.org/browse/JBEAP-588.