I suspect that this is an "improvement" by someone who likes to see newest posts first, assuming that everyone else does too.

On very active threads, I often find that there are a number of long posts to catch up on since my last visit. Having to scroll down as I am reading the first post I have missed, then scroll up past two posts to get to the top of the next one, and then repeat this whole palaver for each subsequent post, is a right pain.

I don't mind threads opening as sorted descending, so long as I can select 'sort ascending' when it suits.

DC