Windows store has passed the count of 20,000 apps adding more than 7000 apps in past two weeks. According to statistics more than 18,000 apps are free. If this goes with the same rate: Windows store may reach 30000 or 40000 apps by the end of this year.
20000 apps is really a great milestone for any new app store. Developers are now concentrating on making apps for Winodws 8 (a new candidate has arrived in this race; after iPhone and Android now its Windows 8).
Windows 8 sales might not be to the mark as expected by Microsoft, but its increasing steadily. With this rate of new apps coming for Windows 8, for me Windows 8 is a winner and will do good in long run.