what is the difference fundamentally between padding and margins ?
For the differences - Rohan Khandwal has shared a very perfect link.
Would the behaviour differ depending on O.S. and devices?
Now If we are talking about the behaviour of the view which has been given diffrent margins & padding. Then It will definitely look diffrent in different devices with diffrent resolutions.
Thats why we are given diffrent dimen/values/layout folders which have their own meanings.