Apple's refusal to license its FairPlay DRM system used in iTunes to RealNetworks and RealNetworks' subsequent attempt to create interoperability by reverse engineering (which Apple is not happy about) is a perfect example that, in the future, many of the really hard DRM-related problems will not be about copyright law, but about competition law (see here, pp. 619-630).
The short story is that Apple does not make money from the iTunes Music Store, but from selling the iPod. By using DRM and anti-circumvention regulations, Apple can ensure that no competing hardware manufacturer is able to create music players that are able to play songs encoded by Apple's proprietary DRM system. Of course, there are excemptions for interoperability in both the DMCA and the European Software Directive, but it's at least questionable whether they apply in this case.
Just as in the Lexmark and the Skylink cases, DRM and anti-circumvention regulations are not used to protect content producers, but certain business models of hardware manufacturers. By wrapping technology platforms in a DRM system, DRM can be used to control downstream markets and channel innovation. How DRM policy should deal with such cases is not an
easy question. On the one hand, some protection for DRM platform developers
may be desirable in order to provide sufficient incentives for the development of
the platform. On the other hand, such incentive structures have to be carefully
drafted and limited in order to not put too many stumbling blocks along
the path to well-functioning competition and cumulative innovation. Solving
this tension between DRM protection by intellectual property rights and DRM
competition leads to the general problem how intellectual property protection
and competition policy interrelates and interacts. More particularly, it is
troublesome that anti-circumvention regulations are increasingly used in circumstances for which they were clearly not intended.
For more information on the Apple/RealNetworks controversy, see Fred von Lohmann's thoughts here and, for some background on Apple's business strategy, see the Berkman Center's recent iTunes study here, pp. 11-12, 44-48.