Not all of the space marine chapters differed. True, the blood angels and dark angels had different leadership and different flavor units. But they had many units that were identical and that worked identically in both their mechanics such as tactical squads. The chapters became even more identical when you got into successor chapters where it was literally identical in all ways except for paint scheme.
Here we have much the same. Basic core units that have the same make up but instead of all being born into it where it is just a job all of the troops are indoctrinated to the point of fanaticism. The approach to warfare itself feels different. Most see this as going from a grinding machine that just rolls over to a ravaging storm that does it for the sheer joy or destruction and a greater focus on force users apparantly with stormtrooper leaders using light weapons adding a close combat element to their units that was not in the original movies. We have seen several entirely new units that could have existed in the empire but were not shown and at least one that likely was not present then at all. It also comes down to leadership. Different leaders can cause forces to operate in entirely different ways on the field in a game. For example Some can have longer command ranges or cause nearby friendly units to fire or act "out of turn".Phasma has a fear range thing in x wing that affects nearby enemy ships just by being near the one she is on. Thats something that not even Vader had.
To many it could even be how they view their army. A player might just not like the original movies preferring only the new ones and think "well, if they dont have my faction, I'm not even gonna bother playing". It could be a matter of an empire player thinking "I wish they would do some FO stormtroopers so I can use them as empire ones to have a wider variety of poses. We have at least one more movie to go and a few years at least and possibly an edition to go before we see it. I have enough faith in all involved parties (movie makers, game makers and players) to have enough imagination and creativity to make it work and make money doing so.... well at least the first two anyway lol. We have even seen FF create good units of their own that arent in the movies at all to fill gaps to keep factions even and it work out well and look good. Heck, you could even have the Fo be identical in all ways mechancially and not add in any new units outside of the named characters and leadership and I would be willing to bet that there would be people who do not currently play empire buy them to play starting a new army and more than a few current empire players who would just for the variety sake of having their models serve double duty.
Of course, I could be wrong but from what I have seen in practice in the last 35= years of wargaming, It is not likely.
Edited by EVIL INC