There's a difference between the perception of your feed being public, and Twitter selling your feed data to a corporation to utilize for targeting, advertising, reselling to employment agencies in the future long after your stupid teenage profile is deleted, whatever.
When a solid 10% of the users are kids (and a much much larger percentage is entirely clueless) it's worth questioning and the people that do know what's actually going on have a responsibility to ask questions.
That's my best attempt to get fired up about privacy on twitter, you forced my hand - oh won't you please think of the children?
Ref twitter age - http://royal.pingdom.com/2010/02/16/study-ages-of-social-net...
2. What about the people whose Twitter accounts are private?
3. The people 'racing' with each other for followers or retweets are by definition more public than most other people. Unless you are going to claim that all or most Twitter users fall into that category. Trying to use them to categorize the user base of Twitter as a whole seems a bit off.
4. Twitter is a broadcast medium, but what we are talking about are the perceptions of the people using it, not the reality of the situation. There are plenty of people that broadcast stuff publicly that they wouldn't want their parents to read. Why would they do so? "My parents aren't on Twitter." I'm sure the same thing applies to bosses and the workplace.
In most cases it's not at all, here's a good page on the topic: http://www.canyoucopyrightatweet.com
And if Twitter wants to make an extra (maybe morally gray) dime off of any "privacy outrage", they can offer certain users to pay a fee to have their tweets NOT included in these dump.