I think the main economics lesson here is that, in the short term, supply of cabs is relatively fixed while demand for cabs fluctuates. As long as prices are fixed (they're usually regulated), there will be some periods of excess demand and other periods of excess supply. This mismatch involves a cost that economists call 'dead weight loss'. Anyone that's waited in long taxi queues has experienced this first hand. If prices cant adjust to changing levels of demand/supply, other mechanisms (eg queues or fights) will take its place. If prices are allowed to move with changes in demand/supply, this avoids dead weight loss and, in theory, maximises the sum of consumer and producer surplus. Ie, its in the best interests of both consumers (as a group) and producers (as a group).

The issue of producers capturing consumer surplus is probably more clearly illustrated with an example of price discrimination... This is where the cab driver charges a student $10 and an adult $20 for the exact same service.