We have been using MSMQ with Win Server 2008 and now Win Server 2012. As you said it's part of a system and just works. If you are a Windows guy, use it without fear. It is not obsolete.
Just other frameworks/technologies build on top of mqmq. If you happy with the features, then why would you add an extra dependency on RabitMQ or ActiveMQ, apart from more stuff to learn, and more things to fail?