In game app updates, bypassing App Store Some apps, I've noticed that developers are able to update their software without submitting them to the App Store. 

For example, Game of War will occasionally tell you that an update is available and to restart your device.  You can then watch the progress bar carefully and see that updates are being pushed to the app.

I'm assuming they are using XML to change certain attributes and their location on the server.  That's a guess but I don't know.  They are able to make significant feature changes to the game, like adding hyperlinks to map locations,  push sales promotions, add certain events etc. These methods don't require compilation, as that would obviously require resubmitting the app.

What is Apple's policy in the developer terms or seasoned advice on how to keep from running afoul of behavior that would get your app pulled from the store?
I see a lot of games do this and I believe it's OK.

Think of a game as being 2 pieces: the app (program) and the data it runs on. Apps are generally allowed to download and store data.

If an update is merely adding new zones or items represented as various files or tables (with no new programmatic functionality needed), then it only needs to request new static data.

However: game engine updates would require a change to the app and therefore an update via the App Store.