According to this article on News.com, the next version of the iPod update will prevent users from being able to load music purchased at the RealNetworks online music store onto their iPods. Additionally, this "fix" may render previously purchased Real music unplayable on the iPod.
From the article:
It was not immediately clear whether iPods older than the photo edition had as a result also been rendered incompatible with RealNetworks' technology.
Apple is apparently not willing to open up their DRM technology to competitors, a strategy that, perhaps in the future will change, but for now seems to be viewed as a competitive advantage by Apple. When Real first introduced their Harmony system that allowed iPod owners to purchase Real music and load it on their iPods, Apple was not amused, so it is not overly surprising that Apple has made a move to block Real access to their devices.