Is this just visits directly to twitter.com? or does it reflect visits via twitter's api?
I think the original comment was saying that many people strictly use twitter from their phone or third-party app. There isn't much on twitter that draws an established user to the website like there is with facebook.
How this translates into twitter making money, we don't know yet, but it seems like it is the direction they are going with Chirp( http://chirp.twitter.com/ ) and with talk of giving more developers access to the firehose.