I finally figured out why Facebook introduced that new picture interface a month ago. It seemed so totally unnecessary -- was anyone complaining about the old setup? -- and in fact more unwieldy, adding lots of unnecessary code and visual confusion to the simple, self-explanatory earlier version.
As I discovered earlier, the new version has one advantage (for Facebook, anyway): you can't download other people's pictures from it. Go ahead, try it. Right click > Save As. It's not there. Annoying!*
Why would Facebook do this? Well, it does yield small privacy benefits, for starters. Your friends can look at your pictures, but they can't pass them around. No one can download those pictures of you chugging vodka from a frying pan and send them to your boss. Or your mom. With that said, anyone who posts seriously incriminating pictures on Facebook is still obviously tempting fate.
But I'm also sure it's not lost on Zuckerberg and his minions that this change forces people to rely on Facebook to a huge extent.
It's cloud computing with an evil twist: once files are in the cloud, they're hard to get off the cloud. Nobody has the option of collecting pictures for themselves and keeping them offline. Instead, anyone who uses Facebook to share pictures is then railroaded into sticking with Facebook, as long as they want to access those same pictures.
In a sense, I think this might be one of the most aggressive steps by Facebook thus far. For the most part, Facebook's metastasis into our daily lives has been voluntary: the site provided services, and users opted to take advantage of the services. But what they've done here is to actually remove functionality, with the effect of making Facebook even more indispensable a portal into our own lives. They have us over a barrel, and they know it.
*There are workarounds. PrtSc, for one, although that requires you to futz around in an image editor to an obnoxious degree. Also, Right Click > Reload brings up the old interface, from which you can Save As normally. This does seem like an oversight, however, and I'd expect it to disappear eventually.