i'd say because the oxford gray is a true gray. almost exactly what a flannel trouser should look like when you think of a flannel trouser. the navy is a marl, not a solid traditional navy, so a bit (like, extremely marginally) more difficult to match.
to some degree the seat is affected, even if only very marginally. since it's a precut piece of cloth, if you only took in the waist without somewhat adjusting the seat it would just bunch at the waistband seam.
prob. not. are you trying to grab those whiskey LHS on ebay right now?in any case, i'm an 7.5D Barrie and a 7.5D Van and the the Van is definitely tighter than the Barrie. Still comfortable but I could have sized up to an 8D on the Van. the Van really only runs about 1/4 size bigger the US TTS whereas the Barrie, like most other Alden lasts, runs a full half size larger.