Of course they do. That's how an iPod could play FairPlay content without a network connection. They didn't strip the DRM upon upload the the iPod.
I'm sure the Netflix files on your iPad are still DRMed. They just give you some kind of key that's only good for a limited amount of time.
I guess the practical question here is whether that functionality is usable via the javascript API:s.
I'd expect it is if the browser implements the security plugin infrastructure that Netflix (and others) have been pushing.
If they do, they should be able to get this to the web version of Netflix.
(Laptop screens are great for watching video content on e.g. a flight or train ride. Bringing an extra piece of hardware like a tablet just for this purpose seems silly. Phone screens offer poor ergonomy. They are only really a decent compromise on a bus or a subway, or similar.)