Have you noticed that a disproportionate amount of popular software products comes from the USA ?

Examples: iOS, OS X, Phosothop, Oracle, Windows, Final Cut Pro, MS Office, iTunes, iWorks Suite, iLife Suite, AutoCad, Aperture, Google search engine, Twitter and endless stream of software that are the best in their fields and that are the models the rest of the industry want to emulate.

Few people would deny that the most popular software comes from American companies.

Obviously there's plenty of good software coming from outside the US, like Linux or SAP but most great looking, killer software comes from USA.

Maybe these companies outsource the code elsewhere but the inception and design is mostly done in the USA.

Why is that? and, can it be replicated elsewhere given the correct "ingredients" ?