Really, iOS is a stripped down OSX? Perhaps you'll show me how I can access the desktop on my iPad, or how I can run an OSX program compiled for ARM? WinRT is Windows compiled for ARM, iOS and Android were both written for mobile devices. Maybe you should look at the size the OS takes on the device.
And neither iOS or Android will reload a webpage when you go back. Neither does WP8.
He is correct Surface uses Windows NT Kernel and some other userland, as does iOS. Just because the UI is not the same doesn't mean that the core of these are based on their full desktop OS counterparts.http://en.wikipedia.org/wiki/IOS
It's a testament to both systems, showing how portable their code bases are that they can both still switch between different CPU architecture
(Windows NT has always been portable (Alpha & Itanium, DEC as well as some other RISC's) as has the core underpinnings of MacOSX Unix which is all about portability.
As for the lag, im not sure i haven't used a Surface yet so cant comment. I think for the majority it depends on what your doing at the time, sometimes my Android (GN 10.1) and my iPad have lagged when changing orientation, most of the time it's pretty instant. The surface problem sounds like it can be fixed through further updates anyway as the hardware doesn't seem to be that underpowered.