It's an unusual feature that i don't think i have seen in other games. That is not a complaint, just an observation. I can understand teh point of view that a scout moves into an army and then stops to move at the same speed as the army, but i think it is important to have scouting units that can rove around  ahead of the army and dip back in and out of it as needed, which is the customary role of messenger.

I just find it odd that at the begining of a turn, when no unit in the group has moved, that all units are still limited by the slowest member.  When units break rank from a group which hasn't moved, I think each unit should have all of their movement available. 

Sure sure. 

And what cockamamie justification can you come up with for units that are stationed in a city?

Just assume that no matter what move your unit has normally, it will have 2(or FSM forbid, one move point, if you have children in the town) on a frequent basis. Just assume your army won't move faster than 2 and plan accordingly.

Keeping units together for combat bugs were fixed, but the downside is that any unit exiting a stack (including emerging from a city with other units) only gets the movement points of the slowest unit).  This obviously can fix some pretty bad exploits but it's a little annoying.  At least you get free movement when exiting a city (1 square free).