Given that the current complete.zip is 19.1MB, I'm not sure that's the best way to work things. Every time it gets out of the browser cache, it would have to be reloaded in its entirety, plus any casual user that just looks at one file would have to wait for the 19.1MB download before anything would happen.

Having said that, while ldraw.org does in fact host all of the official (and unofficial) part files on its web server in a fashion that would allow automatic download, ldraw.org is also fairly slow, and getting the parts from there would probably be quite slow. Also, the last time I checked (which was admittedly years ago when implementing automatic download in LDView), gzip compression was wasn't enabled on ldraw.org, so downloading parts actually transfers all the bytes, even though part files compress extremely well, and gzip compression is standard in http 1.1.