Different size for webplayer and apk

Why when publish with web player .unity3d size is around 2,5 MB but when publish the some app into android .apk size is around 12/13 MB ?
I admit it i not comprime any image and nothig is prepared for mobile, i really put in .apk the same data. I can think that what is not inside .unity3d is inside webplayer plugin…but why this difference!

The web player package does not include the ‘engine’ which is already installed and is larger than 2.5M. So your web packages only contain what your game needs. APK’s need to bundle in the entire Unity game engine along with your game content, as there is no ‘player’ app for Android, but wouldn’t that be cool?

i think right so, if this is the only reason then it’s ok