No, Japanese can invest in other markets using international brokers. I don't know details on the fees and currency conversions. Investing in a foreign exchange is always at a slight disadvantage because of currency conversions and fees.
US stocks are traded on foreign exchanges. Even if you insist on buying on a US exchange, the currency conversion is not very expensive. If you're a buy and hold investor, it won't matter at all.
And yet you often see US people recommending to buy US stocks. There are risks and benefits to buying both domestic and international stocks.