Keep in mind that the Maloofs only own a bit over 50%, so their share is about half of the "sale value" of the team.
Well, I'm not sure I would say the Dodgers' attendance is that poor. Last year they averaged about 36,200 (#11 in MLB) in spite of the McCourt mess and ended up over 2.9M on the season. This year they're up a bit at almost 38,800 per game (#6 in MLB), which is a pace for over 3.1M. In the past several years before that they've been in the 3.7M attendance range so the McCourt fiasco did cause a bit of a dropoff, but it's not like their attendance was terrible or they didn't have a history of massive success in the market.
I think everybody was a bit surprised by the $2B bid on the team anyway. What this really goes to show is that franchise value is what somebody will pay for it, not what Forbes thinks it is. The group that bought the Dodgers obviously thought that they could make it work at $2B, and a lot of that probably has to do with TV rights. For the Kings, well, the debt on the team (ARCO, NBA) looks like its in the $150M+ range, and even shared across all the minority owners that leaves $80M+ of debt on the Maloofs' share. Seeing as the debt goes with the team, I guess they'd be lucky to get $150M for their shares (translates to about $425-450 total debt-free value of the franchise).