Actually if you have a structured storage for files, you sooner or later end up with an image that's just not stored in one file but in severals. Look at what the Zope people are doing with their storage alternatives - there is already one that stores objects as single files in the filesystem. And look at what beasts like ClearCase are doing: the file storage is actually stored in VOBs which are nothing less than images with repository features that can be exported as filesystem lookalikes. Or look at Mac OS X (or NextStep) applications: they aren't single file executables, but several files in specially tagged directories. If you look at what is in there and look at the Windows EXE format, you will notice that EXE files are just the same, only they are integrated into one filesystem object ..
So there isn't so much difference between images and filesystems with structure. There are even ways to map one onto the other. I don't think it would be too big a problem to write a DAV capable webserver in Smalltalk that doesn't export filesystem objects, but Smalltalk classes from the image in fileout format. Not that I am eager to write such a beast, I just think it would be doable - and simple. And with a DAV interfaces you could mount your Smalltalk image in most desktop environments without noticing the difference.