There's two issues here. First is the supply-demand balance, which several commenters have addressed (would you rather have bottled water cost $5 a bottle during Sandy or not be able to find any bottled water because "gouging" law kept it at $1?).

The second is that studies of cab drivers during rainstorms show that cabbies set a goal for daily earnings, and then leave the streets once they hit the goal (causing supply constraints). Would be interesting to see if uber has been able to address that psychological response in any way (tweaked incentives that give an additional bonus for driving more per month, rather than per day, for example).