"You're not wrong Walter. You're just an asshole." - The Big Lebowski
Yes, technically MS has the right to ban people from the service for any reason. No, doing so before an already shaky launch is not a good idea, especially when the user in question was generating positive interest.
Let's play the hypothetical game of the update patch that he downloaded is not a final release. Guy is humming along, pumping out good info, and everything looks great. Boom, system crashes, hangs up, or something to that effect.
MS has to combat this damage, to what is essentially an internal beta, not meant to be seen or used by the general public. That is potentially more damaging then knocking a guy off the network until the console and XBL is ready for the general public.
Likewise, MS (and by default Sony & Nintendo), have the right in my mind to ownership of the initial release information prior to launch. It allows them to build anticipation, and guide the narrative as they see fit. The are not going to let a leaked console derail that, and rightfully so in my mind.