Hell, it's only about 45 million in the US (assuming you believe Twitter's own numbers - which I definitely do not).
So at best, you're getting 1 in ~8 folks in the US. More realistically, I'd assume your audience is more likely 1 in ~20 in the US - assuming you manage to get literally everyone to follow you.
Is that larger than you're going to get on your own site? Probably.
Is that everyone? fuck no. It's basically no one. You're reaching the worst 5% of the country - those who have nothing better to do than browse twitter, or those who are using twitter to promote themselves.
The brief exception to this is politics - where Twitter was an easy way to get a relevant soundbite from a politician on a topic. I think that era is waning very quickly.
Most media sources aren't embedded in small forums.
