I have seen Continental do it a few times. Where they would board Coach first before First due to the same issue. I think I have also seen Delta do the same thing. At least they are trying to get an on-time departure of the flight. Think of it this way. They could make you sit and wait for first class to board prior to boarding the entire plane. I was flying a couple of weeks ago JFK-SFO and they did the same announcement that they were boarding by rows in coach after first was done but they did at least give Elites the ability to board the aircraft before they started calling rows.