I think it's just an artifact of pre-tablet era interaction design (not that this software was actually written all that long ago).
Nowadays it seems perfectly reasonable to imagine clicking and dragging the image around in order to pan -- I'm not confident that particular interaction would have even occurred to a lot of people a few years ago, though.
I would say: Pre Google Maps era. I find it perfectly intuitive to click and drag most online maps around, but it might have been weird the first time I encountered it.
For example, I still like to scroll down to go down in a web page, and get confused (and frustrated?) when I use the new mac mice which use the touch-screen/map type scrolling. However I'm quite sure that if I was a mac person, I'd get used to it fairly quickly.