The disclaimer is somewhat influenced by events that happened in this developers first game, Acting Lessons, and the reactions it got. I think he wanted to make it clear at the start of this game that everything wouldn't be sunshine and rainbows, and sometimes it shows. While this game has so far been fun and lighthearted for a large portion of the episodes we played; he still touches on some issues that could depress people. He likes to make a fun game but one with serious elements as well, and we never know when he may decide to ramp up the drama so he's just letting players know in advanced. As Mormont mentioned above me in his post; he touches on topics like depression, drugs, poverty, bullying.
Its an awesome game though. Great characters, tons of funny dialogue, plenty of hot women to choose from, and sexy moments. As I mentioned it is lighter than his first game so definitely jump in and give it a try. Most who do have been loving it so far.