[Bobblehead]

With respect to the Post article, Americans selling American stock will not affect the value of the US dollar. That is influenced by foreign buyers; for a British firm to purchase Microsoft stock on the NYSE they need to purchase American dollars to do so, and that increases the demand for the US dollar. Bill Gates selling his stock may result in Microsoft shares decreasing in value (because of an increased supply) which may actually entice foreign investors to buy US dollars so they can then purchase those shares at that price (if they believe it is a good deal). It all depends upon why Bill Gates sold - if it is because he thought the value of the stock was about to go down then you may be correct and this is a bad thing. If he sold because he wanted the money for some other purpose (like buying something else he believes is undervalued) then it may be a good thing.

It is long know ploy for a country to try and lower the value of it's currency (which maked the goods produced in that country "cheaper" to the rest of the world, and should increase exports). If done on purpose, this is known as a "Beggar-thy-neighbor" policy. Policies like these tend to require 2+ years before their true or full effects are known (but like the speed of business, this timeframe is shrinking).

Macro-economics is still quite a new study, and there have been many differing theories proposed in the last 50 years, but like many of the social sciences, no single unifying theory has emerged yet.