The Erlang packages in Ubuntu are slightly different from the ones in debian. Ubuntu's Erlang packages have debug information stripped out to make them smaller so that Erlang and CouchDB can be included on the LiveCD. If you are a developer writing software in Erlang, you probably want to have Erlang files with the debug information included so that you can more easily use the debugger and tools such as Dialyzer. You can get Erlang packages built with debug information from the erlang-dev PPA. This PPA also has backports of newer versions of Erlang.