release schedules are always subject to change
Exactly. Studio release schedules are often very fluid - especially ones that are announced more than seven months out. Films can be and often are shifted around, added, and removed. Much of the time an announcement such as the one that Variety published is merely a snapshot of what the thinking was on the date it was released. Much of it will in all likelihood remain the same - but some of it has a real possibility of changing sometime between now and the end of 2011. That's just the way the industry works...
Now, none of that means that the Depp/DS film will definitely be released in 2011. As far as we know, there's still too much about production of the film that's up in air to have any concrete idea when it will be released. But at the same time, that announcement in Variety doesn't necessarily mean that the film definitely won't be released in 2011 either.