I'm pretty sure we are getting way off topic here but OK:

It is about how dependant two products are on each other, and if that could have been avoided if you had chosen another design approach even if you didn't like it. Mr. Shahzad will tell his customer that he has a solution in the form of his telephone box. The customer buys it, and then finds out that it only works in places where line reversal is implemented. And that you can not get line reversal everywhere which makes for a box which works in one building, but not in another.
If Mr. Shahzad had gone for cadence detection, the product would have worked almost everywhere, except maybe abroad.

The comparison for a TV would be: this TV is a colour TV, but the colours have to be activated by subscribing to the special colour service of the cable company. Other TV's don't need that to give color.

The comparison for an PC would be: after having been connected to the internet, this PC will think it's still online forever. To be able to really log it off, you have to subscribe to the ISP's log-off service. Other PC's don't need this.

My customers are always right... well, almost ;-)