There is actually an MIT study that says that one possible way to kill bitcoin, would be for big names to create a coin as well, and we would end up being with a coin for almost every service that's available to us. A facebook coin, a google coin, an apple coin, an amazon coin, etc. Those coins would be completely different from BTC, because they would be centralized, but I do agree that if those services would be able to convince people to use them, by offering advantages on the services they provide, it could become a threat to BTC.

They would not offer any advantages over fiat, except for commodity and "promotions", but I guess that most people don't really care, and they would use them for sure. People will never understand the true value of bitcoin until a global financial disaster happens.