Q. I'm curious: What regulations and/or software restrictions prevent one from using a "flexible date search" function for international travel?
A. That would be the US Department of Transportation. They asked that Travelocity include those often hefty fuel surcharges in their international fare results; but Travelocity said that they didn't have the technology to do this, since these and other taxes and surcharges are calculated when exact dates are chosen by the consumer. But now, Travelocity is indeed showing international flexible date search results on some major routes, but not all. Seems like the list is growing day by day.
You can use flexible date search for international travel on Orbitz.com to almost anywhere, although Orbitz does not have all of the low cost international airlines such as easyJet and Ryanair; on Travelocity, you can do international flex date search on some routes.