no insulation in attic

We purchased our house about 3 months ago. We had a home inspection. Winter hit and we noticed a significant difference in the temperature of our first floor master bedroom. It is between 8 and 10 degrees different than the rest of the house. We had the a/c guys come out and check the system and our ducts. After additional inspections, it was determined that our master bedroom has no insulation in the attic above it. The home inspector did check that attic access. It was in plain sight and easy to get to. Is he responsible for looking in all attic access or just one?