Is it necessary to put high mileage oil on cars over miles?

Yes ... and ... no. Engines with lots of miles might be better off with a synthetic oil as synthetics have less friction, and less friction means less heat, and possibly better/longer engine performance. Be careful out there though ... there may be scrupulous people who want to sell you some 'special oil' at a very special (high) price that could be nothing more than normal engine oil. I myself use 100% synthetic oil in my car, and have been since the day I drove it off the car lot when it was new and that was 12 years ago and now nearing 150,000 miles and NO engine wear or problems.