For example, once upon a time building a superior web browser was hard, because the moat you had to cross was that Microsoft would always prefer their own browser, so Windows created a structural barrier to adoption of new browsers. So the amount by which you had to be better than Internet Explorer back in the day was critical, because if you were just a little better you would never get enough adoption. You had to be much better or convince Microsoft to lower the moat.

Bringing up a new stock exchange was another protected industry -- the incumbents had built a huge regulatory apparatus around themselves which meant that to compete with the incumbents, you first had to comply with a lot of regulations which were themselves molded after what the incumbents were doing. Exchanges like BATS took a long time to clear that hurdle, and many exchanges never made it there, even with superior execution technologies, and were consigned to be dark pools instead of lit markets.

Theoretically social networks have had the moat of the "network effect" of having a large user base -- Facebook is useless because all your friends are on MySpace so there's no reason to switch, and MySpace is useless because all your friends are on Friendster. The implications here are that incumbents protected by moats are fragile; once the moat is crossed they can no longer compete because they've languished, so get eaten alive (as the two examples here or say traditional taxi services).