private void btnDeleteRows_Click(object sender, System.EventArgs e)
{
  dataGrid1.Focus(); 
  SendKeys.Send("{DELETE}"); 		
}

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemWindowsFormsSendKeysClassTopic.asp

This was obvious once I found the class responsible, but took quite a bit of searching to locate.  MSDN article has the code strings for the non-visible characters.

Send a KeyPress Event to a Windows Form

C#