Also, Marvel can farm their characters out to several
studios: Spiderman (Columbia), X-Men (Fox),
Paramont (the various Avengers heroes). DC are
stuck with WB.
Personally that's a streangth for DC as all under one stable should give them more continuity and control. For some reason though DC have never tried to use this streangth and instead seem to refuse to use the bigger picture with their movies. We just end up with a collection of movies (and TV shows) from DC which are stand alone and where the charachters have no connection to each other rather than all existing in a single universe.
While Smallville is obviously not the best example you just have to look at the way they mismanaged the use of Bruce Wayne and Jimmy Olsen while also preventing the use of other charachters forcing Smallville to create almost identical ones. Highlights the general mismanagement of the properties which WB seem to be trying to move away from