The examples you give are simply not comparable. In all three cases, this was not someone throwing a ton of money at something and copying it to try to steal it.
Google was made by two grad students who came up with a better way of searching. They invented a superior product and it took off on its own merits.
Gmail was largely created by one person helming the project on his own, and again it took off because it was VASTLY better than existing options. I was a Gmail beta user-- I remember! It wasn't even close.
Facebook, again-- not a corporation throwing a ton of money at something. It took off on its own, exactly as depicted in The Social Network. It was made by a handful of college students and people simply loved using it in the beginning.
Given your examples, you see to have misunderstood me as arguing that a successful product can never be replaced or lose its dominance. Of course I am not saying that, that would be crazy. I am saying a corporation or any other entity with a lot of money cannot replace a successful product using that money. They can only do it by actually coming up with a better solution to the problem, and that almost never happens-- they simply aren't able to do such a thing in most cases.
Instead they deliver hollow, branded imitations like the many examples I named, and they fail.