28 days later, and a dollar (or several hundred) more

Q. Why are international airfares from the US so much more expensive when trips exceed 28 days? My wife and I have noticed, for example, that Tampa to Paris is about $833 from February 15 - March 15, but an additional week (returning March 22), the price jumps to $1,172. This seems to be the case no matter what dates we put in -- if we want to stay more than a month, the flight is considerably more, and it applies to any airline we try.

A. Unfortunately, sale fares are geared toward the more casual vacationer, who's going for a short week or two, and theoretically needs to be given extra motivation to purchase. The airlines figure that someone who's going for a long stay (and whose travel habits are more commuter than tourist) is going to be willing to pay the higher fare. This is a case when one might have better luck checking out consolidator fares.