Completely agree. Facebook does something that is easily replicable, they've just managed to market themselves better than anybody else. But even that is starting to fail them as people are beginning to turn against the behemoth that is Facebook.
Meanwhile, Google has amassed so much positive public relations with their self driving cars, fiber optic work, and being against SOPA/PIPA, that it's not even funny. Combine that with the practical and diverse nature of everything they have a part in, and you have a very, very solid company.
Apple will probably always be Apple, they too rely heavily on marketing, which will run out at some point. They will also have a bit of a tough time as more people switch operating systems and move to Linux (I hope this happens).