Having access to a large internal market allows you to grow to a fairly large size while still only serving that internal market. Then, when you want to expand abroad, you're likely in a much better financial position to take on the expenses of dealing with lots various local laws and regulations.
... (I would add to your statement) with a large amount of median disposable income. Adding to this, a large numbers of consumers who have access to consumer credit and are far less reluctant to purchase on credit than other nations.
A lot of countries have a large internal market but not all of them actually have the purchase power or the inclination to spend on novel non-established products as much as the US market.
Moving from the west coast to Germany was definitely a fair amount of culture shock there. Americans love trying out shiny new things that are weird or different, my experience has been that Germans are much more cool to that kind of thing. They're simply less interested in novelty for novelty's sake.