oil change and tire rotation tip

now here's something of high interest.  according to big O tires, you should get an oil change and tire rotation every 3000-5000 miles.  but when i looked at my car manual, it said to get an oil change and tire rotation every 7500 miles.  that's a big difference.  of course, it works to big O's advantage if you visit them more.  i'm just going to go with what my manual says.