The Layout is looking as expected on the phone and looking different on the emulator. I am using SDK API 10 (Android 2.3). The test phone is a Motorola Milestone with Android 2.3.3 (Cyanogen Mod 7).
The SDK layout preview renders the preview like the Emulator.
The following image shows the expected rendering on the right side (rendered by phone) and the unexpected rendering on the left side (SDK API 10, emulator and preview).

What is the reason for the difference and how do I fix it? Removing margin and padding (by setting it to 0dp at TextView1) did not help.
main layout (parent)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/test_bg_red"
android:padding="20dp"
>
<include
android:layout_width="fill_parent"
android:layout_height="26dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
layout="@layout/test_child" />
/>
<include
android:layout_width="fill_parent"
android:layout_height="26dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
layout="@layout/test_child" />
</RelativeLayout>
child layout
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="26dp" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginRight="4dp"
android:gravity="top"
android:includeFontPadding="false"
android:text="42"
android:textSize="32dp"
android:textStyle="bold" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/textView1"
android:layout_toRightOf="@+id/textView1"
android:includeFontPadding="false"
android:text="TextView2"
android:textSize="12dp" />
<TextView
android:id="@+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView2"
android:layout_alignParentTop="true"
android:includeFontPadding="false"
android:text="TextView3"
android:textSize="10dp" />
</RelativeLayout>
I believe this is caused by different screens having different aspect ratios. Since phones have 4×4 cells regardless of physical screen size, each cell must be wider or narrow to fit 4 in a row. Using DP takes care of density, but screens which are more or less square will still require cells to be more or less square. That means the number of DP per cell will vary and cause your views to not look the same on different devices.
The only solution I have found is to make your layouts as flexible as possible.