IIRC, rows 1-8 on the outbound (I assume eastbound redeye from east coast) are blocked because they're offered as part of the "Snooze Zone" service, which is basically take off, have a nightcap and go to sleep. Very limited on board service, which is what most business travelers want on the short flights to LHR. You typically can only request these seats at online check-in or at the airport. I recommend it - you can have a full meal in the lounge (on departure, AND arrival), where the food is much better than what's served on board anyway.