riak_kv uses gen_fsm, so people looking for a real world use case could check out their usage: https://github.com/basho/riak_kv/blob/master/src/riak_kv_get... https://github.com/basho/riak_kv/blob/master/src/riak_kv_put...
I'm a relatively new to Erlang, but being familiar with gen_server made it pretty easy to understand the gen_fsm docs and figure out what was going on. I don't see the exclusion as a big deal.