Yeah, basically some time controls have a given amount of time per some amount of moves, so they need a way to show that in the second half, you just have a flat amount of time to finish. So for instance, in the Ohio Chess Congress (State Championships) it's 40/2 SD 1. So you have 2 hours to make 40 moves, and one hour to play out the rest of the game. Keep in mind that generally long time control tournaments take alot longer to finish, and are harder to book for TD's, since they have to ensure enough interest and find a site for that long, and pay for a site for that long. It may not be that long time control tournies are dying, but it's just that they are harder to put together. I know Ohio has about 4 biggies that are around the same time every year, with maybe a couple of other smaller ones.