I've been a wee bit out of the loop recently, gotta love tax season, but I've been doing some catchup reading today!
The way I see it, in an ideal world there would be NO empty flights on any carrier, leaving the US/other longhaul destinations and heading back to the UK. At least not while there are still people stranded away from home. For situations like this, there should be some sort of seat pooling system for all airlines. If Delta have 4 seats left from JFK to LHR, Continental have 3, BA have 7 etc etc and Virgin could fill those seats then they can buy them for a set amount, and get an extra 14 people home a day or two earlier, rather than paying extra nights accommodation and food. Obviously that's an extremely simplified explanation, but with reports of planes heading back to the UK with empty seats, and people still stranded with estimated departure dates a week or more away, there must be a better solution.
Also, I can't remember off top of my head, how many planes was it VS sent off to long term parking? Are they still there, and how long does it take to get them up and running again. Would it have been financially viable to get them flying again, at least for a week or two, to help with this situation?