I've read a post where someone has said they have no advice but they don't want to read and run. No one can see how many people have read a post and not replied. On UK Parents it would show the amount of views and the amount of posts.
When it is on a bereavement thread or one where the OP has gone through a terrible time it seems so churlish and very self serving. If you don't know what to say but want to give sympathy or support then say I'm sorry, post flowers, offer practical help but don't say don't want to read and run on a serious thread.