Semifinal pairings set for BNP Paribas Showdown for the Billie Jean King Cup

Serena Williams will face Kim Clijsters and Svetlana Kuznetsova will play Venus Williams in the semifinals of the BNP Paribas Showdown for the Billie Jean King Cup, exhibition event to take place March 1 at Madison Square Garden in New York.
The semifinal pairs were determined according to the 2009 year-end rankings. The highest-ranked player was paired with the lowest ranked, and the remaining two are to face each other.
The exhibition features no ad scoring format, and each participant will compete in a one-set semifinal with the winners advancing to a best of three-set final.

so because serena won, australian open and wimbledon, it goes to the winner of the previous wimbledon?
Jacob, what are you trying to say?
Kiaha, I think they chose the Williams sisters firstly because the audience in New York is interested in seeing them the most, and secondly because of their recent successes.
I think Jacob is talking about who will win the exhibition…
no, i'm talking about, why was venus chosen, when she didnt even win a slam?
Jacob,Billie can do whatever she wants with her exho and she seems to like Vee a lot.
Oh, i see. so, she chooses?
Jacob, I think she does, or at least plays a large role. I think they primarily think of the attendance, which players are likely to attract the audience.
The places go to the last 4 people who won slams I think so Serena, Kuznetsova and Clijsters and then Venus was the last person to win a slam besides those three at Wimbledon 2008.
So that's the principle. Then JJ was a black sheep last year.
[...] were having a discussion here on Women’s Tennis Blog as to how they chose players for the one-night exhibition event at [...]
Okay so the initial participants are chosen by the grand slam winners of the year, Serena, Kim, and Svetlana. Then Because they need a 4th, Venus would be the most obvious choice option, because she was the last person to win a grand slam before those 3 players and was a grand slam and YEC finalist. Because Serena drops out, the next previous grandslam champion before Venus was Ana. There makes perfect sense. If another drops out then the next alternate should be Maria Sharapova.
Tennis fan, thank you very much. I think we have completely resolved the principle now.
It's all about marketability and ticket sales and box office draw. Don't forget sports is a business. The Williams sisters are a ticket draw. I would have replaced Serena with Maria Sharapova or Jelena. Maybe they were not available so they went to Ana?
There was one person that told us here that Maria and Justine rejected to take part, but I saw no confirmation to that story.
[...] long-awaited Billie Jean King Cup in the BNP Paribas Showdown took place on Monday night in New York and the winner is seven-time Grand Slam champion Venus [...]