Taxis are also independent contractors. Not every taxi cab must be wheelchair accessible to comply with the ADA. Therefore it stands to reason that Uber's drivers don't necessarily need to modify their cars to comply with the ADA. I will concede that Uber drivers have a requirement to make a reasonable accomodation for disabled passengers.
It still isn't established if Uber's drivers really are independent contractors. But if they are, I don't see how Uber is in violation of the ADA. Individual drivers may well be. And Uber will need to sort things out if it expects people to continue to sign up as drivers.
There's a lot of things that suggest Uber to be an employer, but the rides themselves seem very contractor-y.
Taking a percentage fee for putting driver and customer together leans away from employment, in my view. There are a lot of types of middlemen that are not employers.
I have a fun experiment. Let's ask the IRS if Uber's drivers truly are "independent contractors" as they argue, despite the regulations they impose on drivers which are surprisingly close to regulations you'd impose on an employee.
This has happened before, with costly consequences (Fedex Ground attempted to (illegally) label its drivers as independent contracts: http://www.washingtonpost.com/news/storyline/wp/2014/10/23/h...
At least as far as federal tax is concerned, the IRS has some advice at http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employ... and http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employ... .
The IRS probably already knows about Uber. They probably haven't audited the company or asked for details, but they must be vaguely aware of how the company operates.
But Uber is breaking the ADA.