Most of us know that Regen decreases with a full SoC, but that doesn't explain why it needs to apply service brakes over a spec'd g force of braking. Yes, I do get less regen with a full battery pack, and no my car does not apply the service brakes (2015). However, any vehicle that can slow at a higher rate, being able to signal that it is slowing is important.
I think, that someone is mis reading something.
No reason that a vehicle that has less regen doesn't need auto service brakes and one that has more capability does need it!
The important thing is the brake lights, and having installed more than a few Jake Brakes and Telma retarders, and read the instructions, it did mention that some jurisdictions require brake lights when the retarder is activated, and actively retarding. Regen, is nothing more or less than a retarder.