The other thing to consider is this, since your question concerns sites for paying clients: People who turn Java and/or JavaScript and/or cookies off are probably more tech savvy on average than people who don't. So it's entirely possible that people who turn Java and/or JavaScript and/or cookies off would have higher average incomes than people who don't. It would be interesting to see someone do a survey of this; if an income difference were shown to be true, such a result might lessen the enthusiasm of clients for creating sites which require these technologies in order to even work.
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Actually, accessibility when advanced features are disabled is addressed in item 6 of the W3C Accessibility Guidelines, so it's not just for the disabled.
The other thing to consider is this, since your question concerns sites for paying clients: People who turn Java and/or JavaScript and/or cookies off are probably more tech savvy on average than people who don't. So it's entirely possible that people who turn Java and/or JavaScript and/or cookies off would have higher average incomes than people who don't. It would be interesting to see someone do a survey of this; if an income difference were shown to be true, such a result might lessen the enthusiasm of clients for creating sites which require these technologies in order to even work.