No STW & MTW have the same death and dying sounds, similar others as well. RTW had updated sounds.
Battle system? You mean the one from STW & MTW? The reality is that when RTW came out it was EPIC FAIL on the battle system because as you will note even a fully patched version of RTW (Not BI) has significant problems with the pathfinding with unit grouping maneuvers. This wasn't an issue in with the previous games. What made RTW standout and get sales was the 3D units and scale. It was really self marketing, but I'm sure "Time commanders" and the History channel's "Decisive Battles" had a lot to do with it. Still a good game though.