How does skype distribute the data for the number of people online?

In Skype where it says 15,279,670 people on line, how do they distribute that data. Do you think it's distributed peer-peer or do you think every client does a lookup to skype.com every 10 minutes or so? If all 15 million clients are doing a lookup to skype.com every 10 minutes that's a maximum possibility of 2160,000,000 requests a day... But even if it's only a fraction of that it's a serious amount of requests just to distribute a number!