It's been like that for a while, certainly as long as I can remember. They do a similar thing on long haul flights. They're basically charging more for what they perceive to be 'more desirable' seats, more desirable could mean any manner of things but in your case it could be the extra space or being closer to the front of the aircraft and therefore quicker to deplane, or something more nebulous. Whether or not it's worth it is down to you and what you feel the value to be.