As someone already said, I'd imagine it's purely a cost saving measure. It's all well and good us relatively computer-savvy people looking for them (I have a 450W one myself), but the vast majority of machines I've seen in the past few years with these have shipped with the standard mains cable for the monitor. Maybe it was cheaper to stock twice as many standard cables than 2 different IEC cables, or maybe they figured they weren't getting used in the majority of cases, but it is most likely cost cutting, cos for an ATX to switch off the power to the monitor it needs more than the switch on the front; it needs an entire power switching circuit, which is maybe an extra 5 or 10 parts. Addto this the extra cost of a M-F lead, and this is huge in a tightly competitive mamrket such as PSUs and home PCs.
