Many of these ladies charge more per hour than your doctor, dentist and lawyer do. Do you tip these professionals who've spent a lot of time and money on schooling in order to be competent enough to take care of your needs? I'm guessing no.
So why should you tip a provider? Sorry, if a lady making 300+/hr can't put forth her best effort during an appointment without the prospect of a tip, then she should find something else to do. And clients who see ladies who believe that they are entitled to a tip are getting played IMO, because she definitely isn't enjoying herself as much as she says she is.
For example someone at Maddy's price range should not be complaining about money at all. I can't take her reasoning seriously either. Being an independent provider is a very profitable job. Marginal costs are low, so if a lady is able to cover her fixed costs (phone service, verification/advertising fees, incalls, etc), she nets a significant amount of money. If accommodating special requests is too expensive, then don't do it unless the client is booking a multi-hour appointment. (Of course, Maddy, you probably don't need the business advice, but FWIW).
The only exception I would agree with is a top-notch provider who charges much less than the city average for comparable service. This would be something outrageous like a 150/hour lady who gives the type of service that's normally worth 400/hr.