Ok, I guess a serious response is in order.
I posted the explanation from a google employee who worked on android (it is still there on her g+ account) a while back and NO ONE read it. Reading is hard, I get it.
In layman terms, everything in android is an activity. That activity, if it involves an interface, has a separate window (all activities and windows are sandboxed btw). Tap on an address bar? The keyboard showing up is a separate activity opened by your OS, in a separate window. When it comes on, you see the animation of the "keyboard window", but its hardly noticeable.
And this is where it gets interesting. Any app that involves UI elements which need constant redrawing (and hence constant window animations) WILL create a burden on the hardware unless it is powerful enough. THIS is why powerful hardware is so much more important, to run those windows and their openGL and webGL contexts. Current hardware is powerful, but a lot of stuff going on can still overpower it.
The way google tackles it is they build a cache. Say you are scrolling a list, all items are then pre-cached upon launching the list. So they only draw one "window", the list UI, say a contact list UI if you are in a contacts app. Scrolling simply fills the pre-cached items in the window instead of redrawing it with new data again. However, if you tap on "contact details" the contact details window (and a separate activity) will open. Good hardware PLUS good coding will make this process seamless.
Now here's the thing, the above seems to explain why skins lag when scrolling with lists and other UI because OEMs are probably not getting the hang of it.
And this is because google gives tremendous freedom to a dev. You can make your app flawlessly smooth, or a disaster. This is a double edged sword. Same like in iOS. Xcode already provides easy layout and coding tools, at the expense of flexibility.
And by the whole nature of separate sandboxed activities, android is in theory very secure, except the fact google allows apps to interact if given permissions during install. THIS IS WHY YOU DON'T GET A VIRUS WHEN VISITING A SITE ONLY ON YOUR ANDROID DEVICE.
I think an easy to understand example is contact list in TW. When I was scrolling it on a gs4 with 50+ items, it was grinding along. What I noticed was that after I turned off that air hover think that tries to follow my finger, it was smoother.
The gs4 all of a sudden was freed from that extra task, that extra activity, and having to render another window showing me the preview. Hence less work and smoother scrolling.
I hope this was helpful, as much as my lame attempt of making things easy to understand goes lol.
