Excellent explanation on balancing the rod, but I have to disagree with you with the bait caster rod not being able to adjust the balance on them.
Both bait-casting and spinning rods can have their balance be adjusted. The orientation of the reel seat has little to no effect on the balance of the rod. The same can be said with the weight of the reel you slap on it, they would not change the balance of the rod. Just think of it as a seesaw, no matter what load you put in on top of the fulcrum point, it does not affect the balance or load on any end points of the seesaw. The fulcrum point in rods will be where you are holding it, which is right where the reel is seated