There are many biographies on WP that do not mention the birth date of their subject. That doesn't mean this info should not be there. There is currently not a single Good or Featured article on a journal, so you can find examples in both directions. (Science (journal) is only a C-class article, nature (journal) has a rather generous B-class rating. Among participants in the WPJournals project, there is consensus that this information is important, even crucial.