Whether a job requires a PhD or not depends on level of responsibility and the perception of the employer and/or his clients. I do not think there is a discipline that requires a PhD. Certainly data mining can be learned and an employee can do productive work without a PhD. This depends more on the person, his or her ability to learn quickly and adapt as well as being able to understand the literature, than on previous education. This is especially true for data mining which is an evolving field. So even the data miners with PhDs will have more to learn as time goes on.