Hi @ThiloS
Most of the hypervisors today support VXLAN. So one may chooses to run vxlan in all DC environment, starting and terminating on the servers. In this case you will map the vxlan to an EPG. Note that ACI supports encapsulation of VLAN, VXLAN, as well as NVGRE:
But since most of environments are still running vlans, it makes sense to have the examples showing the vlan based encap.
Stay safe,
Sergiu