To the down-voters, I tried to Google some data and the best I could come up with is that 63% of the top 100 software companies are in the US [1]. That isn't 90%, but I said it was a wild ass guess, and there's no denying that the US is by far the biggest software producer.

[1] http://www.softwaretop100.org/global-software-top-100-editio...