I don't know if Android has the feature where you just tap the status bar to scroll to top but iOS does. With that feature I'd rather nav bars just stay at the top of the page, I'll just tap the status bar if I need to get back up there, which is almost never anyway.
Android doesn't have that by default, you need an app for it, and I'm pretty sure you also need to be rooted. Definitely not something you can depend on users having.
