It's been the case for awhile, although it was not always. As one of the possible culprits, I assume it was to prevent those hotly engaged in 'debate' from using it to watch their for favourite idiot respondents every coupla seconds, while they themselves browsed elsewhere, so they could then devastate them as fast as their pathetic reply appeared. I suspect it could really overload the servers, since 'New Posts' searches the entire board, to do what a 'Refresh Page' could do from within the Politics Forum.
If it encourages more measured, thought-out replies that reflect less choler and more wisdom, it won't be all bad.