Newest was [replaced with oldest][1] because it doesn't break bottom up viewing of questions that have multiple pages of answers. There was a bit of debate about which to have, since they're basically redundant. Others have [expressed profound grief][2] over its absence, but we're not very likely to change it. 

As this would affect every site, this is something you'd probably want to propose on Meta SO as a feature request if you have a strong use case for changing it back. I'm declining it here to keep it from appearing as an open feature, that doesn't mean you shouldn't propose it there - just make sure you have a strong use case.


  [1]: http://meta.stackoverflow.com/a/75301/50049
  [2]: http://meta.stackoverflow.com/questions/134259/bring-back-the-newest-sort-order-for-answers