At this moment, everywhere you look (mainly the privilege page and a load of past meta posts), it'll be saying that you'll be getting your next privilege at 2000 reputation total.
While it's true that the gap from 1000 to 2000 is only 1000 points, it makes talking about privilege thresholds a lot harder. Right now I can shout a number (10k privilege, 25k privilege) and a lot of people will know what I'm talking about. Talking in increments isn't nearly as clear-cut, and might even confuse people that aren't as good with mathematics or English.
Communicating privilege levels in increments will likely lead to more questions like some of the ones we already have about badges. I'd expect some other user to come wandering by and ask "I have 1200 reputation, yet the progress bar is showing I only have 200 out of 1000. Is this caching?".
Unless the way sites talk about privilege thresholds changes to also talk about increments. But again: This will likely be more confusing. There's a difference between saying "you get privileges at 5, 15, and 50 reputation points" and "you get privileges after your first 5 points, then after your next 10 points, and then after the 35 points after that". The first one is simpler and more direct :)
So it makes sense for the progress bar to communicate that you're at 1200 out of 2000. Bonus point is that it is a bit less depressing than a nearly empty bar ;)