Only if you buy all of your wines at a supermarket. I have no problem buying wines not owned by these companies. The wines that Robert Mondavi produced were spectacular. I recently had a 1987 Reserve Cab that was still bright and alive and still had another 10 years to reach its peak. When he launched Opus One he created a wine that all other Napa wines were to be measured against. At its best, it was the greatest wine coming out of Napa. Unfortunately, today other wine makers are handling these wines, and it shows. The latest vintages of the Reserve Cab and Opus One are watery insipid wines, and sully the reputation of the man who put California on the world wine making map.
Opus One had a few good vintages LONG ago. Since they expanded the production and started outsourcing the fruit it went downhill fast. Over-rated and over priced. I've never met anyone who thought Opus was better than Mondavi's best reserve cabs. JMO.