It is true in some ways but there are people who dont speak good English that have been successful. My ex mother in law is successful running her own business dealing with international relationships with South America and Mexico and her English is very weak.
You're right. A while ago, I read an interesting article in Bend Bulletin' Business Section Newspaper that if you own a business... You will get more customers if you speak more than just English. For example, on that article, a car dealership who can speak both English and Spanish... One mexican immigrant arrived Bend, Oregon from Mexico... He wanted to purchase the truck but he struggled to communciate with many car dealers because he doesn't speak English very well... He almost gave up and went to different car dealership... One dealer came to him and spoke in Spanish. He got very impressed and able to communciate with him very well and purchased the truck. After that, he told his relatives about that dealer... More and more mexicans go that dealer to buy more vehicles. That dealer sales are skyrocketing because of that.
As for me, I use ASL all the time to communciate with people... Once I discover any worker in any place that I go to knows ASL, I always return to that place because we can communciate and I feel that workers are very loyal to me and treat me equal. Its felt really good.