Maybe my math is wrong but...
The average price of electricity in the US is 2008 was around $0.11kwh.
At that price, $160 would buy you 1455kwh.
Even drawing the full 737watts, that represents 1974 hours of play... or 82 days.
If your rate is $0.20kwh it's still 800kwh, representing 1085 hours of play, or, 45 days.
Sounds to me like they were also giving the toaster oven a good work out toasting hot pockets and tater tots! Maybe they took the xbox and played it outside every night and forgot to shut the door behind them?