Which is how advertising people speak, no? Horses for courses! (ie it's appropriate to the context as "newspeak" is kinda what advertisers deal in)

Rosie the Riveter, Apple's 1984 comercial, the energizer bunny, Transformers. The amount of creativity that goes into advertising is both amazing and heart breaking. The creative part of advertising truely is creative, even if applied to such a dull task.

I’ve never seen data on this, but I often wonder if advertising is where artists generally find the best income potential.

Guess you haven't seen Mad Men? It's Don Draper's department name. They say it all time referring to the team who creates the ad ideas.

I guess not more than all other jargon? I guess they need a way to differentiate the images/etc from the campaign itself.

It's new to me. I did some research on Urban Dictionary (lol), and the definition for the usage of "Creative" as a noun was defined there as early as 2004. So I guess it's a usage that's been known for a quite some time.