Those ads used to upset me. They made it look like health food. Yes, a lawsuit seems a bit extreme but how else can a company be made to stop false advertising? Not like a consumer can write them a letter saying "please stop making those claims" and a company will stop running an ad they spent big bucks to make. A lawsuit though, they listen to. And that can make other companies think about their claims before they create ads.
And yes, consumers should read labels, but I doubt very many do. In fact, I would say that most don't and I imagine most people think reading labels is something that is not easy to understand so they don't bother.
As far as the "frivolous" MacDonalds coffee lawsuit goes, I used to believe it was a ridiculous lawsuit until I read the details. The amount she was awarded was only two days worth of coffee sales for the company. And that was later reduced. The woman who sued successfully was one of over 700 people injured from the coffee who made claims against the company. And most importantly, the company finally lowered the temperature of their coffee. http://www.slip-and-sue.com/the-famous-infamous-mcdonalds-coffee-spill-lawsuit-revisited/
Unfortunately, sometimes a lawsuit is the only way a company will listen.