I think most reasonable people would agree with what you said.
I'm a heavy Xbox 360 user. I haven't been banned from XBL, because I don't go out of my way to break the TOS. I have been banned (for two weeks...once) from xbox.com, for posting something some unnamed moderator didn't like. A few of my friends have been (temporarily) banned from XBL for things like having "FFTW" in their motto.
In all cases it was impossible to get the exact reason for the ban. When I was banned from xbox.com I couldn't even send a private message to the moderators asking about why I was banned, because the ban removed my ability to PM the moderators. In all cases the bans were handed out anonymously, with no information about how to escalate if you felt you were banned erroneously. People were basically left guessing as to why they were banned with no way to find out what the reason really was. This is consistent across the board with Microsoft.
If I don't know why I was banned, how am I supposed to correct my behavior? Not knowing also often leads to all kinds of unhealthy speculation, paranoia and conspiracy theories.
Why can't Microsoft just tell people? They have all the information about why they banned someone after all.