Any time Disney notices people consistently requesting a specific room type or room location, they tend to add an additional cost for that room. Makes perfect sense. From what I understand, there was a time when they did not charge extra for a pool view, but since so many people requested them, they realized they could put a premium charge on those rooms. It does tend to distribute guests more evenly throughout the World.
I agree that the Nemo rooms have the neatest decor. But I am not sure I would want to stay in one again. Our room was first floor and faced the pool. We had a nice view and the room was conveniently located, but the room was so loud - even well past midnight. Like other preferred vs. standard room options at Disney, you often trade convenience for sleep quality. Since Disney doesn't yet charge extra for "quiet" rooms, I am guessing most guests choose convenience over quiet.