For starters, it's cheaper to manufacture a single piece of hardware than it is to have two different versions. Both versions have the same internal hardware, it's just a matter of the 5 channel option being enabled if you pay for it. Oh and of course you could have various options for how you setup a single channel pager, and having a multi-position knob allows you do to that. Open monitor, tone alert, tone/vibrate alert, on/off duty, different sets of tones per knob position, etc.