It might help if you think of it as directing the camera instead of moving the image. When you click and drag left, you're telling the camera to look to the left.

That mouse panning convention has existed for at least 15 years in most web browsers. Click the middle mouse button to activate it in any web browser.

Not true at all -- then the view follows the cursor as I move it. On this site, the view moves towards the cursor when I click. Very different.

I don't understand the difference between "following" and "moving towards".

Not on firefox-17.0.1-1.fc17.x86_64.

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.

Drag to pan has been around for decades now. The inverted acceleration-style interface was designed to accomodate a joystick.

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.