Presumably, twitter.com is by definition an "official Twitter app." So if you follow a web link to a tweet while logged in or authorize with oAuth, you've used

Presumably, twitter.com is by definition an "official Twitter app." So if you follow a web link to a tweet while logged in or authorize with oAuth, you've used an official Twitter app. Given that possibly expansive criterion, 90% is on the low end of what I'd expect.