David Gerard wrote:
There was some coverage of this matter in WP:BLP - that only noteworthy details of a noteworthy person should be included. (The hypothetical example given is the subject having had a messy divorce - for a minorly notable physicist it's probably not relevant, for a politician it may have been a widely reported scandal.)
I this more than by subject area, it varies especially by fame of the person. For famous people, all aspects of their professional and personal lives are interesting to historians, who attempt to construct a full picture of their lives, tease out possible influences and motivations, and so on. You would be hard-pressed to find a book-length biography of a physicist or mathematician that fails to discuss their personal lives, for example. For less-famous people, it's not notable because frankly nobody really cares about them: since nobody is interested in teasing out possible influences and motivations, we don't need to know any of that info.
-Mark