This might sound a dumb question, but I really wonder and don't know the answer.
I googled, but couldn't find anything worth.
There is usage statistics of Google Play Store: http://developer.android.com/about/dashboards/index.html
Does Google still support these API versions?
I'm really surprised about this situation.
Could anybody tell me the reason?
almost every android phone now has support for 15. Google still supports these, but it is hard to support these old versions a lot of the time, which is why most people don't bother supporting anything below 15. The amount of new people you get is not worth the hours put in trying to support the old versions. this is why most people update to 15 as soon as they get a chance