That's strange -- that should work as you describe, but the URL you provide (from the catalog XML) doesn't actually point to anything.

There are other downloads at various points in the image repository -- you can select Download and then Download Images from individual imaging sessions.  There's also a Java downloader for the images if you select direct download rather than .xcat.  There have been issues with Java recently so you might have to reduce your Java security settings to get this to run.  We are looking into installing an updated version that will work with higher security settings, but unfortunately this is still in progress.