Fundamental questions about your world setting

Some great posts got me thinking about one of the fundamental questions of a world setting - Thought of the Day: A World Without Heroes (The Alexandrian); Disease and Disaster in Hammerstein! (Dr Bargle) and Medieval England Did Not Have Dragons (Monsters and Manuals).

The question being, if gods, magic and monsters exist and affect the world, just what does this mean?

I don't know my answer yet but my initial thoughts, for my medium-fantasy setting, are -

• Some disease is natural, most is supernatural. But actually what does this matter to the world, as they've not had, and may never have, Edward Jenner or John Snow?
• The intelligent (playable) races were created, although at what stage of progression I've not yet decided. Were the first mages / shaman living a stone age lifestyle, or later than that? I'm a bit vague on my Tolkien, but I think he had elves born into Middle Earth in quite an advanced stage.
• What's the dynamic between other intelligent races (here I'll include the less-smart humaniods, such as ogres), and monsters (here I'll include dragons, at the risk of offending). My thought is that the former compete with the playable races, in the same way that different races and realms compete. The latter are rare (although they need some way to come into contact with the adventurers) but not so rare that your sheep are safe.

My other thought is, the setting is unusual that has a pre-history. Most I can think of - game and novel - exist only in the now, unless the past is just there to provide ruins to explore. Exceptions spring to mind - Tolkien, Joe Abercrombie's The First Law trilogy and Paul Kearney's Monarchies of God - but equally most settings exist for a very long time at a medievalish level of development. Is this laziness, or again supernatural?