Netflix isn't discriminating. They're selling a product. Whether that product is of use to someone with a particular disability is going to decide whether or not they purchase that product.
If you're deaf, and if you know that you're not going to get captions out of something you purchase, are you going to buy it? Are they going to require that every single thing that is bought or sold in our country specifically accommodates deaf people?
By that nature, are auto manufacturers going to be required to provide cars that can be driven by the blind? Is Nike going to have to make shoes that can be worn by quadruple amputees? It's a slippery slope when you dictate what a company is or is not allowed to sell.
Without closed captions, a video is not as valuable to someone who can't hear the attached audio. At that point, a decision can be made to purchase or not purchase the product. Netflix isn't fraudulently claiming that their videos contain captions when they don't. There is no barrier that stops people with disabilities from purchasing their product. There is nothing that stops people from using their own third party software to convert speech to captions.
With that in mind, people who are hard of hearing or deaf have a choice. They can purchase the product, which is advertised as is, or they can choose not to. The ADA requires that accommodations are available for accessibility of stores - it makes no claims over whether the products said stores are selling needs to be what people with disabilities would want. Otherwise, Wal-Mart would be in violation for selling pogo sticks, because clearly, a quadraplegic would not be able to use one. Barnes and Noble would be in violation for selling books, because illiterate people who are such because of a learning disability would not be able to read them. Certainly Best Buy can't sell car stereos without requiring that they have a display that shows all of the lyrics of every song they play.