Yes, there's no standard, but:
The Brits adopted the LMT MWS (takes the .308 PMAG) and the US uses the KAC M110 (takes the .308 PMAG). It would make sense that most of the aftermarket support would follow what's currently being produced in large numbers to fulfill government/military contracts.
Yes, you're right in that there's a metric ass-ton of different AR-10 pattern .308 rifles out there. After purchasing my LAR-8 and dealing with all sorts of charging handle, stock, and magazine compatibility issues, I should have just gone with a SR-25 pattern rifle. For example, I use the BCM Gunfighter charging handles on my AR15s, and was disappointed that they did not make one for my LAR-8. Indeed, the only enhanced charging handle for the LAR-8 is the PRI Big-Latch, which besides being expensive, has a reputation for breaking the roll-pin. Thus, I purchased the latch handle only and added that on to my LAR-8's stock CH...
I'm just trying to pass on lessons that I've learned. YMMV.