And yet, people do grow up knowing that the green banana button means "phone" and the notched rectangle means "save", and often never even question "is there a real world analog for this icon?". It isn't that icons are obsolete: it is that we are graduating from a language of pictograms to a language of ideograms, yet for some reason we have large numbers of people telling us that that is somehow a horrible thing to do.
One explicit advantage that these sorts of icons have is that they allow for a nice symmetry between Save and Open icons and upload/download icons (Glyphicon is again a good example; see glyphicon-open and glyphicon-cloud-download). This ties into another, perhaps more arguable advantage, a blurring between local and remote save actions. As applications become increasingly web-based, device-independent, and portable, it makes more sense to me to intentionally separate the "save" action from it's destination; I don't care so much where or how my data is saved, I only care that it's save and that I can get it back later.
I'd love to hear responses to my thoughts here; they sort of developed as I wrote the comment, so they're rather fresh at the moment.
It's a really difficult problem. So many of the things we do today are done on a rectangle with a screen. That doesn't make a good icon. Maybe icons are obsolete altogether?