The article isn't focused on students but I still think this covers some of the possible reason's it isn't as common in the U.S. (of course this is just a broad generalization) -
http://www.cnn.com/2011/TRAVEL/02/04/americans.travel.domestically/I would add that I think a second/third/etc language through school is more common outside of the U.S..
FWIW I personally know quite a few Canadians who did something along those lines (although admittedly some of the families I'm thinking of weren't necessarily looking for deceleration due to gifted issues - they just wanted their kids to experience travelling).
We are pulling our kids out of school for a month this year to travel and are planning a larger trip in the next couple of years. If they were struggling (or being challenged) in school we would schedule it around school rather than purposely giving them a break from school.
