You are 100% right. When I managed a Good Year auto center, we often had training by major oil companies and one of the major oil suppliers told us that the cheapest store brand oil is no different than the highest price brand. In fact the only difference you will see is if you run your oil over 8,000 miles than you can see a little more break down in the cheaper brands.

We were instructed to tell all customers to change the oil every 3,000 but when I always told mine that they could change it every 5,000-7,500 miles. I guess my honesty payed off because I had one of the largest return customer base in our region.