The common rebuttal is: "You are making the mistake of calculating on the Margin, you forgot to calculate E Fixed Costs"
But, I think of it somewhat differently:
It is rarely the case that you _have_ to use Product A at Price D, but you still do, which means it usually has more value to you than Price D - and is it that unreasonable that Company B should charge it's customers what their customers value product A at?
I know I would.
As a side note - I've managed to get most of the people I SMS with frequently into using WhatsApp, and, once I see that I've sent less than 100 SMS messages for at least three or four months, I'll shift it over to my Data Plan.
Apple will likewise have simliar impacts when they bring their SMS alternative online.
So - the free market does respond to this in a semi predictable and reasonable manner.