There's some basis in buying weak in this case though, because worlds governments nowadays cooperate closely in their monetary manipulations: they buy or sell eachothers currencies when speculators sell or buy too much of specific currencies. For example, if speculators swap euro's for dollars, weakening euro, strengthening dollar, US planners buy euro's and EU planners sell dollars, directly. The opposite of speculators actions.
Goal is to make sure that not any of their currencies gets outside their allowed rate limits.
Of course, a speculator has to do this before the central planning thieves "correct".
A peg between currencies, such as the Swiss Franc to the Euro some years ago, serves the same goal.
This central planning strategy is also a prelude to a single common currency, see Euro, although for a world currency they consider it probably too early (they want to give people the chance to get used to the idea first, as to prevent them reacting too much), and as long as that is the case they want to give at least some illusion of monetary competition, abit just like political parties, they all pretend to conflict eachother, especially before elections, but when camera's gone they're close buddies, goal to lure people to vote "within" the club as a whole.