Whether or not the list is a true manifesto straight from the horse's mouth isn't really important, but it just makes things more interesting. Plus, it just seems in line with several speeches I've heard from him stating essentially that.
This one produced for AFI specifically comes to mind.
Not only has someone kindly shared the list on a Google doc, but they've also gone through and highlighted all of the films on Sir Steven's list that are available on Netflix Instant View. Check it out here.
People seem to be upset that it's American-heavy and that there are virtually no modern classics on there, and that there are a lot missing that they think belong on there. Well, that's fine. These are movies HE recommends. If you want validity in your complaint, watch the films on the list and THEN you can criticize it and make your own list.
So how many have you seen from the list? My number is pretty shameful, at just under 40, with maybe another dozen or so that I've seen parts of. It looks like I've got a nice homework assignment to do.
EDIT: After a few days of the list being live, there is now a small disclaimer at the bottom stating that the list is debunked but still remains a fantastic list for film enthusiasts looking to learn the building blocks of storytelling.