The reason to not include the full portal is that Fedora has very strict rules regarding the software that can be included: all the software included in Fedora has to be built from source in Fedora itself. We did quite a large effort to have all the components required to build oVirt, but we are still missing GWT (Google Web Toolkit), which is required for the oVirt admin and user portals, and a challenge in itself. So we decided to include only the backend and the REST API.
Our goal is to have everthing in Fedora, but it will take time.
With the upcoming 3.1 oVirt release we plan to make the Fedora official packages compatible with the upstream oVirt packages, so you will be able to install the official Fedora packages and then, on top of that, the admin and user portal packages from the upstream oVirt release. Something like this:
# No need for additional repositories:
yum install ovirt-engine
# Configure the upstream oVirt repositories and then:
yum install ovirt-engine-webadmin-portal ovirt-engine-userportal
Eventually, when GWT is in Fedora, we will of course include the portals in the Fedora repositories.
Hope this clarifies it a bit,