My guess (given just the information on this page) is that for those positions, the payroll system has a monthly wage. That's pretty traditional for exempt salaried employees. Of course, one can't easily convert the minimum wage into a monthly wage given the variation in the number of business hours per month. So the system would have to be re-programmed to handle an hourly wage for these employees with all of the check-printing, taxation, reporting, etc issues that would entail...not to mention the difficulty of handling employees who kept switched ... probably twice ... from salaried to hourly. (Hmmm... wonder if they'd now become covered under FLSA.) Could be quite a big job in any programming language.
Of course, in my scenario if the controller wanted to be cooperative, he could just have suggested that their wages be set to a monthly wage that met the maximum a minimum wage person could earn and thus follow the spirit of the request within the bounds of the system. However, the article makes it clear that this is not the case.
I was caught in a similar situation when I was first hired by my current employer. Their payroll system uses a monthly salary, cutting checks twice monthly. My offer letter for a sort-of post-doc position stated an hourly wage. The payroll clerk entered this hourly wage into the monthly salary box, thus resulting in a surprisingly low first payroll check!