There is a clear difference between 'discriminating' against someone because of their disability, and a person's inability to participate in something because of a disability.
Later in the law discrimination is defined, and it gives an exception that auxiliary aids must be provided, except when providing them would be an undue burden.
If I were Dominos (I'm not a lawyer, so I probably have this wrong), based on a reading of the law, I would argue that since Dominos offers pizza ordering through the telephone it is not depriving anyone their services if the website is not accessible. The service Dominos has to provide access to is delivery of pizzas, not the use of their website, which only exists specifically for the purpose of ordering pizzas. Could a library be sued because a specific book doesn't contain braille, when the same book is available in braille? What if Dominos had two phone numbers, one that offered teletype and one that was voice only? This judgement seems to imply that they could be sued unless both their phone numbers offered TDD, because they are depriving people of the use of the other phone number?
I'm all for making websites accessible, but I find it hard to believe someone who orders a pizza over the phone is being deprived of 'equal enjoyment' of the pizza.