Cars are better built now so they are less reliant on maintenance. Also, I would not consider 120,000 miles high at all anymore. Maybe 40 years ago, but not today. I'd say high mileage to me is 200,000 miles. Even people who don't care about cars like college girls/young women I know have Camrys with 240,000 miles and they don't even know how to fill up their oil.
Thanks to better manufacturing and tighter tolerances in addition to more advanced fluids and parts materials, even maintenance parts and fluids have a longer life. For example, changing spark plugs at every 30,000 miles is a thing of the past. Even economy cars now come with iridium spark plugs that have nearly a 100,000 mile lifespan.
However, if you want your car to go beyond 300,000 miles from regular use, it's still going to require more meticulous care.
I occasionally read bout cars that have 500,000 to a million miles on them and the thing they have in common is meticulous maintenance schedules. Nearly all also run synthetic motor oils to prevent sludge build-up and engine wear.
I prefer synthetics not only for the better protection and cleanliness, but because it also extends the oil change interval. That's important to me since I change it myself and without a garage, I hate working on the car in freezing temperatures outside. Syns allow me to change oil in the fall, skip the winter and change oil again in the spring.
That being said, new cars can get boring as there is not enough to tinker with and fix. That's why it's fun to have an old beater or project car that always has something to do on it. The old and unreliable VW bus fits that bill.
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