Google etc may be a US based company, but they can leverage emerging markets just fine.

There’s a stronger argument to be made for small caps, but stock buybacks allow any company’s stock to effectively experience exponential growth even with flat earnings. IE there’s little long term difference between buying back 2% a stock every year and ~2% actual growth every year assuming you never hold the majority of shares. (as in 1/0.98 ~= 1.02)