I suspect that this was the main reason why Facebook wanted users to use the browser instead of a native app (and why the app is being launched more than 18 months after the iPad was first launched)
However, the proliferation of native 3rd party apps meant that users weren't using the browser to get to Facebook and that may have led Facebook to finally decide to release the app.
[edit1: To the downvoters - I didn't say that sandboxing provides 100% privacy protection. However, it does prevent Facebook from knowing which other sites you've visited, it prevents them from telling search engines who you are etc.]
[edit2: To Xuzz and others: login to facebook on your iPad browser, log into a website that collaborates with Facebook, you'll see that Facebook is aware your visit to the website. This won't happen when you're logged into the app (instead of being logged in on Safari)
Regardless of the downvotes, this is a matter of fact.(in fact, it was recently discovered that Facebook can track some of your web-browsing even if you had logged out)
Btw I made no assertions about "attacks" and I have no interest in debating emotional outburts such as "Please stop assuming everything Facebook does is out to personally attack you or your data".