That's just wrong. According to a test – admittedly somewhat unscientific, but good enough for our purposes – done by developer Benjamin Mayo and vetted by TNW, third-party apps only contribute to ~25% of twitter's activity. Tweetbot is in the upper echelons of that 25%, but it's not even in the top 10 overall.

I'm sure they do well, but they definitely don't have a monopoly.

Sources: http://benjaminmayo.co.uk/how-many-people-use-twitter-s-own-...

http://thenextweb.com/twitter/2012/07/23/only-an-estimated-2...