Joseph is right; however, we do not know where you live and drive. If you fill the car with cheap 5W20 non-synthetic oil and drive across Death Valley in July fully loaded, you will cause considerable engine wear. This is of course an extreme case.
If this was my car I would use 0W30 full synthetic (such as Mobil 1) which is good all year round in any part of the US, including Alaska. This will give you both good mileage and maximum engine life!
As others pointed out, the CAFE mileage standards are largely driving the oil recommendations. Honda sell a lot of trucks and SUVs and has to start worrying about fleet average fuel economy. My Toyota is a 2007 and the recommended oil is 5W30.
Agree your mechanic needs a refresher coures inn modern engine lubricants.