Whereas there are already a lot of websites providing download links to Windows 7 RTM DVD ISO images, the links for the updated versions that have an integrated Service Pack 1 are brand new. Using a scanning script to browse the files on the Digital River servers, I came across these new ISO images more or less by a lucky guess. The advantage of the new images would be an up to date Windows installation right after the initial setup, without the need to download and install hundreds of updates afterwards.
See the complete list here.