JIRA http://jira.jboss.com/jira/browse/JBAS-3513 is a request from a partner to only log a WARN instead of an ERROR if a webapp with the distributable tag is deployed in a non-clustered environment. This allows the exact same webapp to be deployed in clustered or non-clustered environments without generating an ERROR log. The downside of course is if the environment was meant to clustered and there was some problem, they'd only get a WARN.
Either way, the app deploys using the non-clustered session manager. So this is just an issue of logging levels.
I'm about a +0.5 on this. They are pushing for this for 4.0.5 as that's what they'll integrate in their product.