Amy Berg: The difference between a baby writer and a showrunner is enormous with regards to both responsibilities and expectations. The only real job of a baby writer is to take the episode they've been given and make the most out of it. There aren't high expectations for them in the room because of their lack of experience. But if they give you something extra — if they work their asses off by doing research and constantly generating story ideas — they will work their way up the ladder very quickly. A showrunner is the overseer. They're responsible for supervising every aspect of the production. Story breaking, script writing/rewriting, casting, editing, you name it. It's a massive undertaking, both time-consuming and pressure-filled. A show's success or failure is often placed squarely on the showrunner's shoulders. Which is why they need a talented and supportive staff to back them up.
I always find it fascinating how much more egalitarian the system seems to be in the US than in the UK (and bear in mind the shows I've worked on have about a tenth the article's show's budget and rating).
Things are certainly changing here: writers like RTD and Steven Moffat are becoming showrunners (writer/producers in charge of a number of writers) in a way that didn't seem to happen in the past, but on the whole, UK writers, script editors and producers seem to be sharply defined roles that rarely blur into one another (anyone with experience in this area, feel free to correct me).
My experience of writers rooms here, which tend to be for comedy or kids' television, are that stories rarely get 'broken' at the pace they do over in the States - it tends to be a much more fragmented process of 'producer gets a number of the writers together, puts coffee in front of them, nods while they burble, lets them know decisions a couple of weeks down the line', which has its own problems. And to be honest, arguing your corner the way they seem to in this article can often come across in the UK as 'bad form' - you can sometimes be left with the idea that the producer knows what he wants and is waiting for you to come up with the right shapes to slot into the holes he's already made, which can be pretty unfulfilling, although to be fair, sometimes you see the end result and go 'oh I seeeeeeeeeeeee'. But sometimes the only way to show what you want to write in the script is to just... go away and write the script.
UPDATE: Tim Footman asks:
Surely the role of the script editor by definition blurs into that of the writer, to a greater or lesser degree?
Helpfully, they do and they don't - in comedy, a script editor is usually another writer who's been brought in to 'punch up' (add jokes) to a script. In drama, a script editor is a different role: often a sort of assistant producer who points out where they might be weaknesses or inconsistencies in the script, and works with the writer to resolve those issues - although in my experience they very rarely make direct alterations to the script itself, apart from maybe correcting typos, before the script goes off to a commisssioner.
Interview with Joseph Donaldson (BBC script editor on a couple of my projects, as well as Lark Rise To Candleford and Survivors