Fedora 10 - no longer rawhide?

[Timothy Murphy]

Alex Makhlin wrote:

> There is not yet a Fedora 10 distribution but only the beta Rawhide
> (Fedora 10). Here is a great utility I found to upgrade Fedora when new
> releases are available. You will first have to install it.
> 
> as root type:
> yum install preupgrade
> preupgrade

I've read this thread, but still don't understand exactly 
what preupgrade does.
How does it differ at present from "yum update"
which seems to change /etc/fedora-release 
to "Fedora release 10 (Cambridge)"?