why divide it into high and low?

Maybe they found a technical reason... that makes it more reliable as far as tuning accuracy.

Maybe they figure by dividing them... they won't have quite as much TX crystal swapping going on. (since only half the frequencies would be applicable to any given RX... And FCC says don't swap TX chrystals...)

Maybe they just figured that by labeling them that way... they might sell more receivers...

No idea why they did it. the Futaba rep may or may not know either...

've never SEEN a problem from putting a high band crystal in a low band RX. I've not heard of problems from it. But I've not heard of people messing with it either.

I have heard of serious problems from putting a Hitech crystal in a Futaba RX... or a Futaba crystal in a Hitech RX (they fit... but have different multipliers so its definitely WAY out. Range check of... may as well have the TX off... it don't work.)