ChrisShaffer and Innocence spoken very same explanation I'd do!
Simultaneous Turns (Execution) needs some
orders concept that RTS (and, to some extent, Civ II and SMAC) already developed: Waypoints, Sentry mode, Patrol, Scramble (for fighters), Transfer, Attack, Charge Attack, Hold position (to last soldier), Defense and Counterattack, Defense and Retreat (if movement points left)...
It's not so strange, is the way real things work (time lenght apart, of course). It's not as any military unit can move at maximum speed then defende itself full strenght against enemy at the end of turn.
With STE we can set ambush, plan realistic blitzkrieg...
It's not as we shift the game on military tactic, simply we can add a full shade of enhancement with a single more click (my proposal: drag unit "line of movement" with right mouse button clicked will prompt a popup menu to chose movement type; using left mouse button the previus movement type will be kept).
About the limit to tactics as "spy, destroy city walls, bribe units, attack the same turn, move reinforcement into city, sell a facility"

you should consider that until very recent communication advance, every war tactic needs some time to be applyed, and often original plan was changed by battlefield unplanned events. War times are dangerous, you know
------------------
Admiral Naismith AKA mcostant