The reason we're moving to the select box for sorting is to allow for sorting of metrics that aren't present in columns. In the past, Joomla had information overload in it's admin tables and in 3.0 we're trying to intelligently combing and consolidate. For instance in the 3.0 Article Manager we've moved the category under the article title and removed some less important columns like Hits. Having the sort select box lets you filter by any of these metrics, and possibly some that have never been available
