Q: What new feature exists with Distribution lists in Exchange 2010 that relates to Outlook Web App (OWA)?
ANSWER: Ability for end users to request to be added to a distribution list. This is done via the Exchange Control Panel (ECP) self service feature. See this URL for more information.
http://www.msexchange.org/articles_tutorials/exchange-server-2010/management-administration/managing-distribution-lists-exchange-server-2010.html