Why aren't prostitutes paid like stadium vendors?

Tonight I watched a documentary called American Pimp. It was fairly interesting although it was difficult to watch the pimps talk so easily about manipulating women. I think I was made most uncomfortable by the fact that I sometimes felt that they were kind of charming. (That was an awkward sentence. Unintentional symbolism? Yup, that's it.)

Anyways, the most interesting thing I learned was the percentage that prostitutes get of their revenue. Zilch. (I'm not sure how exactly they're paid but that much was clear.) This seems like a bad business plan since it gives little incentive to the women to generate additional revenue. That is, in theory the pimps could make more money by giving the prostitutes a cut so that they work harder. Stadium vendors, for example, get paid based on how much they sell. What is different about prostitution so that this business model doesn't apply?

Perhaps the answer is that it's not different and the industry is due for a shake-up from an economics savvy pimp. But street prostitution has been around so long that I doubt a flawed strategy has persisted. Especially when the alternative is so obvious. Thus, I do think it's correct to ask why the commision-based model doesn't apply.

I'm tempted to relate the situation to the one described by Levitt and Venkatesh of crack dealers working for peanuts in hopes that they can work their way up the organization. But there is no up for these women. Or perhaps "up" is an occasional night out with their pimp. (Okay, I'm getting more depressed now.)

Alternatively, pimps may not need to offer a carrot (percentage of revenue) if their sticks (psychological and physical punishment) are effective enough to get their prostitutes to work as hard as they can. I think this is more likely the case. The pimps can easily monitor their prostitutes effort and punish them if they don't seem to be working hard. Both the cost of monitoring and the cost of punishing are probably low. Monitoring is cheap since the pimps don't have much else to do and the cost of punishing is cheap since the women lack other options. (Well, they could go to another pimp but I wouldn't rule out oligopoly behavior amongst the pimps as far as this is concerned.)

Turning the question around, why aren't stadium vendors paid like prostitutes? I think it's likely that monitoring and punishment are relatively expensive. (And, obviously, punishment is limited.) So, anyone have the data to test this hypothesis? (Perhaps a better question is: what data would you need to test this hypothesis?)