The Legend of Korra seasons are going to be fully enclosed story arcs. Due to some slips of the tongue from the creators and just the general attitude of Nickelodeon being incompetent. The Avatar creators are going this route, if only so that if and when Nick kills off Avatar, it is all fully enclosed and no orphan episodes are left out. In fact, this season was to be the 'only' season of Korra. Nickelodeon ordered a second season as soon as this one was finished in production, hence, all the neatly tied up story lines. (True, ordering a few extra episodes wouldnt have hurt, but the creators stated this was for quality of animation purposes)
It may be little known here, but Nick executives tried very hard to kill the original three seasons of Avatar. Anything that threatens the flagship program (ie. Spongebob) is anathema to them. I am aware that it makes absolutely no god damn business sense, but there it is. Seriously, this is a thing.
Luckily, a couple years ago, a new executive (cant remember his name) said that this was a stupid business model and has since fought for more flagship programming, whatever that may be. Still, one guy can only do so much against a room full of stupid.