If you have a strong product with a lot of interest surrounding it,
possibly even some pre-sales.. you will not benefit much from being in a
If you have a startup in "Silicon Valley", and you have enough funding to be there. Then you could use your "premium location" to attract investors to prop up what would otherwise be a failed idea.
I would say that being in the US does help a lot simply because you get access to a lot of infrastructure and supply chain benefits that are not as developed in other countries.
Also placing your self in a "College Town", can really boost your chance of success. The US "college culture" lets you hire premium talent at a very cut rate ( if not free ).