One thing about the life on this planet, there is always something more to learn.
The reason that they have the same scientific name is that they are the same bird. However, there are subspecies. I'll try and paste some more information.
I was unable to include alot of detail explanation about the subspecies and their ranges, so go to http://en.wikipedia.org/wiki/Barn_Swallow.
http://whatbird.com/forums/photos/birdman/