My UI on Xoom looks ugly/Not what it looks like in eclipse

So I'm making an app for my Xoom, just starting with android development.

I've made a few buttons and all that jazz, using the ADT in eclipse to position everything (using the 10.1 WXGA Tablet config), and it looks great in the editor. As soon as I run it on my xoom however, everything is larger - even the title bar is larger, and when I try and compensate for this, by specifying lower dp and sp values in my elements, it just becomes grainy开发者_StackOverflow中文版 and ugly, as if it's not the correct resolution.

Am I missing a setting somewhere?

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I figured it out - I just tried adding:

<supports-screens android:largeScreens="true" android:anyDensity="true" />

to my manifest, and now it looks awesome - can anyone explain to me why though? I don't really understand the theory.