Actually, in the past, America was a powerhouse because the business of America was business. Government stayed out of the way as much as possible.
So it was a good environment for business to thrive.
Nowadays, government looks for any reason (or no reason) to interfere with business. So, nowadays, there is no good environment for business to thrive in America.
Which is why we are quickly ending our powerhouse status.
Times have changed. Now a days, international corporations have no problem being in bed with the government and promoting regulations that will harm their competitors.
Hedgetrimmer said it better:
http://www.freerepublic.com/focus/news/2727913/posts?page=215#215