It usually goes there, yes - presumably it was put in Main in error.
Before I've checked two other open threads, including the last one, and when the link is open it shows "Main" dark shaded on top of them.
http://lesswrong.com/lw/h3w/open_thread_april_115_2013/
For the time being I switched it to discussion.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.