It's not the "non-liveable" part, I think it's the vent requirements for things like a tank water heater that uses flammable gas, or your car, or stuff you store in the garage that might be combustible or require venting (paints/solvents/etc).
But maybe because most new Irvine homes use tankless water heaters (although I believe those are gas heated too) and are too small to store stuff, vents are not required in garages.