My point is that they might only be getting 1 /64 from their ISP; or getting a /62 or something small, and needing more subnets anyway. In these situations, you may not have an extra /64 to dedicate to SLAAC for certain devices.

Right. I was merely correcting your statement that SLAAC needs more than 64 bits to work with. But my question remains; do any ISPs hand out smaller delegations than a /64?