No wonder Delta is bankrupt

I'm trying to organise a ridiculously complex itinerary for holiday travel this year, so I've been staring at the very useful kayak.com trying to book flights. The latest, and perhaps greatest example of the totally arbitrary nature of airline ticket pricing is the following:

Virgin Atlantic trip from London to LA, then Boston to London: $1400.
Singapore Airlines on the exact same plane operated by Virgin: $9000.

That's right, you could in theory pay a 5.5 fold increase in price, an extra $7600, just to have Singapore Air print your boarding pass.