That comes down to the quality of AFCAD files, and the third party traffic manager you're using. I can't really fault MS on that - although they could have gotten the AFCAD stuff right in the first place but their scenery is built on fairly old data (my local airport - EGNM - is still in it's pre-2000 configuration of two runways, even in FSX). But coupled with their inability to license use of airline names/liveries/etc I'm not surprised that gate assignment is all over the place. That's what 3rd parties are for though...
Indeed, but it's largely the same kind of situation as AFCAD files, as long as the route is signalled properly with direction markers, then things tend to work right, it's fairly rare that you need to break out priorities and other means of forcing route choice.