It's effectively illegal to transport large amounts of cash in the US. As in cops will confiscate it and you have no recourse unless the "preponderance of the evedence" suggests it has no link to any crime.
There are more examples beyond this, but there may indeed be a trend emerging.
You also risk having cash stolen by border agents when crossing international borders. Many countries expect you to declare whether or not you are carrying more than a certain amount.
Examples:
Italy http://www.businessweek.com/magazine/italys-cap-on-cash-paym...
Spain http://www.bloomberg.com/news/2012-04-11/spain-to-limit-cash...
USA (Louisiana) http://www.klfy.com/story/15717759/second-hand-dealer-law
There are more examples beyond this, but there may indeed be a trend emerging.
You also risk having cash stolen by border agents when crossing international borders. Many countries expect you to declare whether or not you are carrying more than a certain amount.