Major market share usually allows the company some pricing power and some cost savings (economies of scale -- a lower variable cost of components (or services like programming) -- and scope -- a larger base over which to amortize a fixed cost).
Verizon passing 50% penetration in Dallas means that there is no way that the cable incumbents in the areas of Dallas where Verizon offers service have a greater market share than it does. It is also proof that the advantage held by cable incumbents in other markets may not be safe. None of this is good news for growth in cable incumbents' profits -- a fact unlikely to pass unnoticed on Wall Street.
It is less-than-clear that FiOS has been a profitable investment for Verizon, but it is hard to see that it would have been better off harvesting its wireline phone business or deploying a cheaper solution like AT&T did with U-Verse. For better or worse, Verizon is still here and its fiber-to-the-home network may be a competitive advantage going forward.