For me, hot code swapping in an entire Erlang cluster without downtime (for example: make:all([netload]) is one of the Erlang killer features.
But let's reverse your question: What does akka have that Erlang doesn't?
Of course you can add dozens of extensions and libraries (scala, akka, spring, osgi, ...) to Java to try to come close to Erlang. But where is the point? In sum all these extensions are much more complex than learning the simple Erlang language that now has proven for over 2 decades that it can do the job offering top scalability with zero downtime.
