Geektastic: The only instance I can think of where this might be the case is when you do what my wife does and contract as a business to the company to provide services, rather than on an employee basis. Of course they are employing her, but they do so by employing our company not her.
She therefore gets no holiday, sick pay or paid public holidays.
I'm on a contract with a start and end date, and a target to achieve by the end. They pay has been assessed by an independent agency to allow for holiday and use of my own equipment, and is way more than I would get for the same role as an employee. The other key difference is that I can choose which days I fulfil my contractual requirements. These contracts are ok because they allow flexibility for both sides of the contract. The real problem arises at the minimum wage level where employers are using casual contracts to avoid their legal responsibilities.