I know Android OS is a lot better compared to others but why is there app always come heavier when compared with the same app on other OS. I installed "Viber" app on my Xperia and it's size is 7.2MB while it's just 1.5MB on my partner's BB.

D bb version of viber does not make calls. So dats y d size is small

The user interface

android OS is the land of free. so developers are at liberty to put as much rich content in their apps as android hardwares can handle. that is why the android version of most apps you see on other platforms are larger in size

android apps offer richer graphics and better colors although the iOS still does a great job or even better job in some instances

Viber on Blackberry is useless. You can only send text but no voice call or special imagesand characters like Android devices and iPhones. So the features on Blackberry is very minute compared to other smartphones so its expected to be smaller. Android packages are not always large and they are the best when it comes to update too since they update partially and not the entire app itself unlike iPhone.

You can get Viber for PC too here http://phonegist..com/2013/06/how-to-install-viber-on-windows-and.html