OK, I found it. It was, of course, my own mistake. At the end of my onCreate method I was doing this:
// Set the focus to the calculate button so the keyboard won't show up automatically
Button calcButton = (Button)findViewById( R.id.ac_button_calculate );
calcButton.setFocusable( true );
calcButton.setFocusableInTouchMode( true );
calcButton.requestFocus();
So of course, no matter what I did in my xml file, I was overriding it in my code. Instead, I used this to hide the keyboard:
getWindow().setSoftInputMode( WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN );
Which works great.