There seems to be an unsatisfactory gray area between slack technology and misguided editorial practice (assuming better guidelines help create more substantial/enjoyable journalism).
With adequate tools for making the sourcing process as effortless as possible (see Jeremy Ashkenas' and Scott Klein's comments) it ought to remain an optional value-add for publishers: those who don't mind having their sourcing restricted to press releases, effort-obscuring generalizations or PR-driven 3rd party referencing won't encourage technologies that would enable their newsrooms leverage their in-house professionalism, regardless of its potential.
Linking/referencing is fundamental to good, original content, whatever the medium (see randlet's comment). If publishing software won't support easy source accreditation (particularly in a web-focused, hyper-linking context), journalists and editors are going to lose out - either by facing a 'keep my job vs. best practices' drama or by becoming disillusioned with the chance of success their organization has in maximizing the credibility of the staff input going into evolving their brand itself.
Taking their access to low cost, more modern publishing tools as a given, perhaps in more dynamic/educational reporting environments they should exploit software with prompts - asking authors to confirm that their content is 100% lacking of any derivative work, sources, or any mere cursory reference to any other material/commentary out there. This might even help less experienced journalists off-set some of the responsibility they have in bringing new ideas to the attention of their demanding readers ('this is my article, but here's some source curation for you, while I get my story straight'). Of course software that assumes any kind of pedagogical role is just as likely to become demonized by journalists who resent tools for their antiquated inefficiency. There's a fine line.
Services like DocumentCloud are vital in all this. As ilamont points out, there are also practical hurdles to overcome: even if you have the technology and inclination towards sourcing best practices, if you're running an online publication there's still the knee-jerk reaction to want to obscure your primary source, in case it out-performs your own content and thereby undermines your credibility. That's a question of quality and self awareness, though. The credibility loop will eventually hit your property, one way or the other.
