From Windows 7, turn off auto-hide on your taskbar the way you like it.
Open up IE or Chrome.
Tell us what you see.
Now explain to us how you've come to the conclusion that when IE or Chrome in full-screen mode in Windows 7 covers the taskbar, which is supposed to be ALWAYS visible (unless it's in "gaming mode or slideshow or screensaver or movie mode" or whatever arbitrary rule you decide), it's OK and it's expected behavior, but when a Metro-style app in Windows 8 covers the taskbar, it's not OK.
If it helps you to understand why Metro-style apps behave the way they do, just think of all Metro-style apps as running in "slideshow mode" and only in slideshow mode.