From what I heard in 2011, the OSM license change was motivated by legal status of the data in the EU. Creative Commons is seen as an arts license and data could only be licensed and protected through an appropriate data license.
An USA. USA doesn't have 'sweat of the brow' aspect of copyright, so it's debatable if a 'collection of facts' (i.e. the OSM database) could be copyrightable in the USA.
http://www.reddit.com/r/IAmA/comments/lc88a/were_the_google_...