According to April Underwood (who is a “product manager” in the “revenue” division):
As interest in Twitter has grown, our focus has been on delivering better ads for users, not more ads. We believe our system is working well because users like the ads experience on Twitter.
(Emphasis is original.)
Allow me to translate that particular brand of bullshit:
“Don’t forget that Twitter, or the interest people have in Twitter, is continuing to grow. Further, we have chosen to show less ads to users, and instead charge large sums for the few ads that we do show — so mad props to us for that. We aren’t sure if this system is working, but we sure hope it is. One time, at Ad Camp, a couple of users told me they like the ad experience on Twitter — don’t confuse that with liking ads — but it’s still very encouraging.”
The rest of the article is an advertising wet dream.