For the E3 and E4 options, $24.5 and $27 you will also get additional software licenses.
Both options will include the ability to install 5 instances of Office Professional Plus per user, E4 will also enable the Lync Server On-premise.
Not only Office can be license and extended to the devices a user has but also on the telephony side, E4 will enable to PBX replacement and adopting Microsoft Lync for phone system.
Again another example how the Microsoft Cloud is mixing and conquering with on-premise deployments, changing the way licenses have been acquired.
The more O365 will offer in the future the more transition from Volume licensing to subscription licensing we will see