This is one of these things that sounds perfectly logical -- you want all UI components to look and behave the same across all applications and all websites --

This is one of these things that sounds perfectly logical -- you want all UI components to look and behave the same across all applications and all websites -- but that is more theoretical than practical. If you built an app that used just what the browser gives you and nothing more, you're leaving so much functionality on the floor. Having more expressive power often makes things simpler -- using more complex UI controls has allowed me to eliminate whole pages from my application. Users are happier and more productive. Browser UI implementations can't do one thing that is vital: compete.