via Shawn Cole:
Part of the problem is that a basic certification for Part 27 does not require an attitude indicator - the requirement for an attitude indicator is often (depends on country) in the operational rules - and only then for commercial operations.
Ditto for things like gyro compass...
Been near 20 years though when i got a helicopter done up for private NVFR it required the full six pack. My understanding at the time a six pack wasn't required for US night heli ops ?
.