Hi Andreas,
This topic is one that has come up internally at least 3 times in the past 6 months or so.
For the longest time, release notes were behind a login on the premise that it would keep information about known issues out of our competitors' hands so that it wouldn't be misconstrued and used against us. There was also an understanding that the RNs weren't useful if you didn't have access to the software they describe. Given that, TAC generally provides release notes to anyone who asks, which breaks that feeling of "security."
I can't say that this discussion is over - there's some things we're working on that have potential to improve this experience and could allow us to publish them openly.
Are there any particular versions you're looking to see? I don't mind sharing them with you if so.
-Drew