Oracle has released update 2 for Java 7, while it appears OpenJDK is still on the original build 147 which was released last summer.
Will/are updates available for OpenJ
I may be wrong, but I think sources can be retrieved with mercurial on a different repository. It seems to be dedicated from the one linked by Peter Lawrey in a comment on the question. The addrees is http://hg.openjdk.java.net/jdk7u/jdk7u-dev
I don't know exactly how branches and tags are managed by Oracle and the OpenJDK contributors, but maybe are the first stable released definitely frozen, and a cloned repo is used instead to ensure inclusion of fixes...
To answer the question, I'm not sure that the OpenJDK sites are supposed to propose any packaged version of the JDK. Oracle's infrastructure is made for that, I guess... I may have missed something, but I think the packaged JDK's that are given on the Oracle website is jsut a bundled, compiled version of the OpenJDK. As it has become the reference implementation, and is actively maintained Oracle, I can't see why it should be different.
EDIT : BTW, I can't find a direct link that I can use to download a packaged OpenJDK on the OpenJDK website, even for the first stable release. But once again, I may miss something obvious :-p
EDIT 2 : I've fixed the link - you know have the link to the repo of all the sources, not only the jdk ;-)
Moreover, as pointed in a link given in the comments, there are many projects under OpenJDK... So the repo structure is a bit complex, with hg "forests" (that I didn't know before trying to compile OpenJDK 7 by myself...).